MacRumors has issued an update of its immensely useful Buyer’s Guide — a consumer-oriented cheat sheet that tracks the update cycle of Apple’s product line and offers informed opinions about whether you should go ahead buy that MacBook Pro you’ve been lusting after or wait for the next model. As MacRumors put it:

Apple updates their products in a very consistent manner. A Mac comes out at a certain price with certain features. The price and features of that particular Mac stay exactly the same throughout the lifespan of the product. So, if a customer buys on Day #1, they are getting the fastest/newest technology for the dollar. The problem, however, is that 8 months later, on the day prior to its refresh, that Mac costs the exact same money, but contains 8 month old technology. (link)

Although based on rumors and second-hand reports, the Guide is pretty dependable, especially since Apple (AAPL) switched to Intel chips. Intel (INTC) is quite open about its product plans, and Apple tends to switch to their newest processors in a fairly predictable timeframe. (Although as MacRumors notes, Intel’s switch to the Nehalem microarchitecture, due late this year, could stretch out some Apple product cycles.)

To see the full 2008-2009 Buyer’s Guide, click here. This is a summary of their recommendations:

• iPod classic: Buy only if you need it - Approaching the end of a cycle
• iPod touch: Neutral - Mid product cycle
• iPod nano: Buy only if you need it - Approaching the end of a cycle
• iPod shuffle: Buy - Product recently updated
• Mac mini: Don’t Buy - Updates soon
• Mac Pro: Neutral - Mid product cycle
• MacBook: Buy - Product recently updated
• MacBook Pro: Buy - Product recently updated
• iPhone: Buy only if you need it - Approaching the end of a cycle
• LCDs: Don’t Buy - Updates soon
• Xserve: Buy - Product recently updated

There’s lots more information in the full Buyer’s Guide, including historical release dates, days since update and links to recent news.

One caveat: you take a risk when you buy a computer on Day #1, as MacRumors suggests. You might want to monitor Apple’s discussion boards for few weeks to see what problems emerge. Let the company and the users who like to live on the bleeding edge work out the kinks before you buy.

What is it about Apple computers that makes them run so hot?

Complaints about overheating notebooks — Apple doesn’t call them laptops anymore for reasons that become obvious once you use them for a few minutes — surfaced soon after the release of both the MacBook Pro in early 2006 and the MacBook later that spring.

Now the problem is the new MacBook Air. Despite assurances from Apple (AAPL) reps at MacWorld that it ran cooler than its bulkier predecessors, Apple’s discussion boards are filled with messages about fans running a full throttle, machines overheating and occasional lock-ups. As of Thursday afternoon, the topic “MacBook Air Overheating” had been viewed 3,135 times and a second topic, “MacBook Air intermittent freezing problem,” had drawn 2,541 views.

“I spoke to Apple and the first thing I was advised to do was to remove all cables and the battery!” one user reported. Whoever was manning that help line apparently was not aware that the battery on the MacBook Air can’t be removed.

On Monday, Apple issued a software update — MacBook Air SMC Update 1.0 — that “fine tunes the speed and operation of the internal fan,” but reports of its effectiveness are mixed. One user said his machine had been relatively quiet since the upgrade. Another said it “didn’t work at all.” Others reported that when they tried to install it they were told that their MacBook Air was already up to date.

The broader problem, one suspects, is that Apple has once again put design considerations ahead of performance and pushed the new machine’s heat tolerance just a bit too far.

The Macworld Conference & Expo, Silicon Valley’s largest technology trade show, opens Monday. But the moment everyone is waiting for comes Tuesday morning, when Steve Jobs makes his annual keynote address at San Francisco’s Moscone Center.

Jobs has set a high bar for himself. At Macworld 2006, he introduced the first Intel (INTC)-based Macs — sparking a burst of sales that nearly doubled Apple’s (AAPL) market share from roughly 4% to something approaching 8% (link). At Macworld 2007 he unveiled not just the all-but-forgotten Apple TV, but also the iPhone — a device that in nearly everybody’s book turned out to be the machine of the year.

What can Jobs do to top that?

There’s no shortage of speculation. The Apple rumor machinery has grown so elaborate that for the second year in a row, Ars Technica’s John Siracusa has published a keynote Bingo card (available in PDF format here and in iPhone format here), with boxes to be filled in as Jobs makes his announcements, introduces his guests and trots out his trademark rhetorical flourishes. (The rules of the game are spelled out here.)

Nobody has yet shouted out “Bingo!” in middle of a Steve Jobs presentation — a moment brilliantly anticipated in IBM’s buzzword Bingo TV ad (link) — but this could be the year.

Some of Siracusa’s boxes are obviously more important than others. A couple (Mac Pro and Xserve) were preemptively filled last week, and there are a few key possibilities that he missed. Watch especially for:

• A Skinny MacBook. Probably the leading candidate for Jobs’ one-more-thing moment, it’s already been named — Macbook air, thin, nano and mini — and imagined in PhotoShop (see here, for example) by bloggers who should know better. Likely specs: 12 to 13-inch. LED backlit screen, under 3 lbs., half as thick as today’s MacBooks, 32, 64 or even 128GB solid-state flash drive, priced around $1,600.
• iPhone updates. A bump in capacity from 8GB to 16GB and maybe 32GB is expected, as well as a preview of the software developers toolkit (SDK) promised for February; we might even get a few demos from developers, like EA, who were seeded with the SDK last fall. A 3G iPhone and a Newton-type tablet are reported to be in the works, but not yet ready for prime time.
• Movie rentals. This is the item Hollywood is following most closely. It’s been widely reported that Fox and Disney are likely to make movies available on iTunes for overnight rental (at $3 to $5 for 24 hours) or for purchase for roughly the price of a shrink-wrapped DVD. If, as rumored, Paramount, Lions Gate and Warner Bros join them, the flood of fresh video content could breath new life into the Apple TV. (The Associated Press reported Sunday that Netflix (NFLX), anticipating such a move by Apple, will offer unlimited monthly video streaming.)
• DRM-free Music. Having famously championed the cause with his February 2007 Thoughts on Music memo, it would be surprising — and disappointing — if Jobs did not use this opportunity to announce a significant expansion of the DRM-free offerings in the iTunes Store, especially after the last of the major labels announced last week that they were putting their music on Amazon.com (AMZN) without copy protection.
• Microsoft (MSFT) Office 2008. No surprises here, since the reviews are already in, but an excuse for what should be the most lavish after-hours party of the show.
• The Beatles. It’s about time. Just in case, Yoko Ono’s John Lennon Educational Tour Bus mobile recording studio is making the trip from its Las Vegas unveiling at the Consumer Electronics Show to be at Macworld. A few hours after Jobs’ speech, there’s a press reception in the bus that’s co-sponsored by Apple.

You already see the flashbulbs popping, right? But is it enough? Apple’s marketing machinery is like a shark that must keep swimming or die. Even if nearly every square on the Bingo card were to be filled on Tuesday, would Jobs have delivered the kind of innovation and buzz the faithful have come to expect?

And then there’s Wall Street to consider. Apple was the high-flying tech stock of year, its share prices having more than doubled in 2007. But as a CNNMoney headline put it on Friday, “What’ve you done for me lately?” The stock fell nearly 30 points over the last two weeks, which could be taken as a measure of traders’ uncertaintly. (Or it could just be a well-timed pause to set up the Macworld effect, the short-term bump tech share prices often enjoy after a Steve Jobs’ keynote.)

No matter how high the bar, Jupiter Research analyst Michael Gartenberg is confident that Jobs will clear it. “This is a company that thinks in terms of strategy,” he says. “Do I think they’ll deliver something as disruptive as the iPhone? No. You don’t achieve that kind of disruption every week; it would be tantamount to getting into a whole new industry. But somehow Jobs always manages to meet expectations, even if the expectations are different.”

To find out how different, tune in Tuesday for Fortune senior writer Jon Fortt live blogging from the keynote at fortune.com/bigtech, video coverage from CNNMoney.com and our post-keynote analysis here on Tuesday afternoon.

Like the Oscars for the technical categories, which the Academy of Motion Picture Arts and Sciences hands out ahead of time rather than bog down the major Academy Award presentations, Apple (AAPL) is using this week to introduce new products that Steve Jobs feels aren’t worthy of his keynote at Macworld next week.

Today it announced two of them:

• A new Mac Pro, with two 2.8 GHz Quad-Core Intel Xeon processors, a 320GB drive, and up to 4 terabytes of internal storage for photo editors, designers and other memory hogs (starting price: $2,799). See here for press release.
• A new Xserve with a standard single 64-bit 2.8 GHz Quad-Core Xeon processor, a 80 GB drive, up to 3 terabytes of storage and an unlimited client license for Mac OS X Server version 10.5 Leopard (starting price: $2,999). See here for press release.