Dueling reports Wednesday from the two leading PC survey firms — Gartner and IDC — confirm what the crowds at the Apple (AAPL) stores have been telling us: The Mac had a great second quarter.

According to Gartner, Mac sales grew 38% year-over-year to edge out Acer/Gateway/PackardBell for the No. 3 spot in the United States after Dell (DELL) and HP (HPQ). IDC recorded slightly slower growth (31.7%) and has Apple still trailing Acer by 2,000 units — not a statistically significant figure in a quarter in which Apple shipped an estimated 2.37 million Macs worldwide.

Gartner puts Apple’s U.S. market share at 8.5%, up from 6.4% a year ago; IDC has it at 7.8%, up from 6.2%. Both reports are preliminary.

Apple still doesn’t make the top 5 in either company’s list of top PC vendors worldwide, although IDC’s Loren Loverde says it came in No. 6. (link)

It’s worth noting that while its competitors were cutting prices to boost sales in a tight domestic economy, Apple managed to grow faster while maintaining profit margins that are the envy of the industry.

And if you count iPhones and iPod touches as computers, says 9to5 Mac’s Seth Weintraub, “you get a whole new ball game.”

Below the fold: the charts from both reports.

It was only seven months ago that we celebrated the 10 year anniversary of what may be Michael Dell’s most famous quote. Asked on Oct. 6, 1997, what he would do if he were in charge of Apple, he told a crowd of several thousand technology execs gathered in Orlando:

“What would I do? I’d shut it down and give the money back to the shareholders.” (link)

The irony, as we noted last October, was that Apple’s (AAPL) market cap was then double that of Dell, Inc. (DELL). Since then, Apple’s value has gone on to triple and, last week, quadruple Dell’s. Here, thanks to MacDailyNews, are the market cap milestones:

• Jan. 13, 2006 Apple passes Dell: $72.13 billion vs. $71.97 billion
• July 27, 2007 Apple doubles Dell: $127.81 billion vs. $63.65 billion
• Dec. 6, 2007 Apple triples Dell: $165.66 billion vs. $54.42 billion
• May 1, 2008 Apple quadruples Dell: $158.66 billion vs. $38.97 billion

By week’s end, Apple was worth 4.04 Dells.

Michael Dell, however, is still worth 3.01 Steve Jobs, according to the latest list of the richest Americans:

• Dell’s net worth: $17.2 billion
• Jobs’ net worth: $5.7 billion

And according to IDC, Dell is America’s No. 1 PC maker, with a 30.9% U.S. market share, while Apple is No. 4 with 6%.

So why the big difference in market capitalization? Apple’s track record of innovation, integration and customer service has something to do with it, but investors pay even more attention to the margins.

• Apple Profit margin: 15.13% Operating margin: 19.28%
• Dell Profit margin: 4.82% Operating margin: 5.91% [Source: Yahoo Finance]

In other words, Dell sells a lot more machines, but Apple makes way more profit on each machine it sells.

A lot has been written about Dell’s third-quarter earnings report, but what caught the eye of analyst Shaw Wu of American Technology Research was its disappointing gross margin: 18.5%, down 150 basis points from 20% a year earlier.

“Controversial and confusing,” Wu called Dell’s (DELL) explanation for these results, especially in comparison to competitors like Apple (AAPL) and Hewlett Packard (HPQ).

“DELL cited a tougher component pricing environment. We find this odd as AAPL and HPQ experienced the opposite and our own supply chain checks indicate otherwise. … It is interesting to note that DELL’s costs may actually now be higher than HPQ and AAPL, something that was unthinkable not that long ago.”

It was 10 years ago that Michael Dell, speaking before several thousand technology executives at ITxpo97 in Orlando, answered a question about what he would do if he were CEO of Apple with a remark he probably instantly regretted:

“What would I do? I’d shut it down and give the money back to the shareholders.” (link)

As others have noted, Apple’s (AAPL) market capitalization today is more than double that of Dell (DELL):

Apple: $140.4 billion

Dell: $62.27 billion

But don’t shed a tear for Micheal Dell. According to a list of the 400 wealthiest Americans published last month, his net worth is more than triple Steve Jobs’.

Michael Dell: $15.5 billion

Steve Jobs: $4.9 billion

[Chart comparing 10 years of Apple and Dell share prices courtesy of NASDAQ.]