“Developers,” a VP at Electronic Arts once told me, explaining why there were so many me-too Windows applications, “will walk through the desert in their socks to get to an installed base.”

True enough. But it doesn’t quite explain the results of a survey issued last week by Evans Data Corp. The headline was that most developers are still not targeting Windows Vista when they write new apps. Only 8% of the 380 developers surveyed were writing for Vista; 49% were still targeting Windows XP.

That makes sense, given that XP still enjoys a 73% market share, compared with less than 15% for Vista, according the latest NetApplications report (link).

What is harder to justify, using the desert-and-socks rule, is the sharply increased interest in non-Windows platforms. The press release didn’t mention it, but Evans Data CEO John Andrews did in an interview with Computerworld’s Heather Havenstein:

“Open source alternatives like Linux continue to take on interest,” he [said]. “As well, MacOS is also acquiring significant interest among North American developers. Although unlikely to displace Windows volume, MacOS experienced 50 percent growth as a primary development platform and 380 percent growth as a targeted platform during the period.” (link)

We’ve asked Evans Data to clarify this quote, because in this form it’s not particularly helpful. The 380% figure sounds suspiciously like a misquote, given that the size of the survey group was also 380. And that 50% increase is unanchored; it could mean 1 more developer writing for Mac or 100.

But any increase in Mac and Linux development is surprising — and encouraging — given that Microsoft (MSFT) still owns more than 91% of desktops, Apple’s (AAPL) OS runs on 7.38% and Linux still hasn’t cracked the 1% mark.

Could programmers be developing an interest in something beyond the size of the installed base?

Apple has no numbers to compare with the 140 million copies of Vista that Bill Gates says Microsoft (MSFT) has sold since the latest version of Windows started shipping in late 2006. (link)

Literally, no numbers. The last time Apple (AAPL) released a Leopard sales figure was Oct. 30, 2007, when the company said that it had sold more than 2 million copies of Leopard in one long weekend (see here). Apple reported $170 million revenue from Leopard sales in the December ‘07 quarter, but that represents fewer than 1.3 million copies. Apple also sold 2.32 million Macs that quarter, more than 2/3 of which probably had Leopard pre-installed.

Even so, the two operating systems aren’t even playing in the same ballpark when it comes to raw sales.

Of course, Vista was greeted with brickbats and Leopard with raves, but Gates didn’t dwell on that in Tokyo Wednesday, where he gave his Japanese partners an update on how Vista is doing. “That’s a very rapid sales rate,” he said.

Not necessarily.

“The most significant number,” says Piper Jaffray analyst Gene Munster, “is Apple’s upgrade penetration vs. Microsoft’s. Apple estimated that about 19% of the OS X user base was on Leopard by the end of its launch quarter. By my math, Vista is used by about 12%-14% of the Windows user base more than a year after its retail launch.”

Apple’s (AAPL) market share slipped slightly last month to 6.55%, according to a new report from Net Applications, while Microsoft’s (MSFT) Windows Vista picked up more than half a percentage point to 7.91% — a growth rate month-to-month of more than 7%.

The Web metrics firm’s monthly tabulations of browser data from the sites of its 40,000 customers offer an imperfect but consistent measure of market share trends. The company’s latest findings are summarized in the table below:

Net Applications offered no analysis of the data, although it’s probably fair to speculate that the small dip in Mac market share reflects buyers holding out for the Oct. 26 release of Leopard.

Charles Jade at Ars Technica’s Infinite Loop points out that this is the first Net Applications report in which Intel Macs overtook PPC Macs. “The transition is over!” he writes.

How did Leopard sell?

Very well indeed. In a press release issued this morning, Apple (AAPL) announced that it had sold or delivered more than 2 million copies of OS X 10.5 in its first weekend on the market. OS X Tiger, by comparison, took nearly six weeks to reach the 2 million mark. That makes the launch of Leopard the most successful OS release in Apple’s history.

“These numbers show the Mac user base is growing,” writes PiperJaffray’s Gene Munster. “It also shows that it is an unusually active user base, with 9% of the approximately 23 million users upgrading in the first four days.” He notes that there were half as many Macs in circulation in April 2005 when Tiger was released, yet it took Tiger nearly ten times as long to reach 2 million sales.

Comparative sales figures for Microsoft’s (MSFT) Vista operating system were not immediately available, but the company is said to have licensed 20 million copies in its first month, a number Leopard is unlikely to surpass. But that’s comparing apples and oranges, given the relative size of their respective user bases. Last week Microsoft reported that it had sold 88 million copies of Vista in nine months, representing less than 9% of the worldwide installed base of roughly 1 billion Windows machines.

More than two years after it was announced, nearly a year and a half after it was shown to developers, and four months after its original spring 2007 due date, the sixth edition of Apple’s (AAPL) flagship Macintosh OS X goes on sale today at 6 p.m. for $129 ($199 for the family-pack).

The authorized reviews are in and they are broadly positive. Boxes containing OS X 10.5 Leopard pre-ordered online have already started to arrive by courier, and according to David Kravets at Wired.com, “BitTorrent tracker sites are churning with the seeding and leeching” of bootleg versions — activity that is expected to stop as soon as the stolen copies can be replaced with shrink-wrapped (and warranty-supported) versions.

And although there were none of the eager buyers camped out overnight in front of Apple retail outlets as there were for the iPhone, crowds are expected to gather as the evening deadline approaches. Tekserve, New York City’s premier Mac reseller before the Apple Stores arrived, has organized a Leopard release party that includes live jazz, iPod nano raffles, a iPod touch for the best Leopard costume, Leopard tote bags and a free Leopard plush toy for all attendees.

Once again, Steve Jobs has whipped the faithful into a frenzy. For weeks, the Apple blogs have been filled with rumors and screen shots and detailed histories of the evolution of key features. Some Apple watchers have already started to list features that were promised in early promotions and dropped from the final release. Unlike Microsoft’s (MSFT) Vista — which was six years in the making — Leopard is expected to be a huge success.

Tomorrow the user reviews will start to come in. Let the praise — and the whingeing — begin.