Microsoft (MSFT) Windows continued its downward drift and Apple’s (AAPL) Mac OS X inched up to a record 7.95% in the market share survey issued Tuesday by Aliso Viejo, Calif.-based Net Applications.

The biggest gain, however, was recorded by the open-source operating system Linux, which jumped more than 16% in June — albeit from a small base — to hit 0.79%.

The iPhone held steady at 0.16%, reflecting a leveling off of what had been double-digit growth as buyers waited for the new iPhone 3G, which goes on sale next week. In a separate survey issued Monday, RBC Capital reported “unprecedented pent-up demand” for the new model. Data taken from 3,600 members in RBC’s Technology Adoption Panel in early June showed that 56% of those planning to buy a smartphone in the next 90 days planned to buy an iPhone — up from 35% in March and more than double the interest in any of the other brands surveyed. See here for more detail.

The monthly Net Applications survey is conducted by sampling browser data from some 160 million visits to websites operated by the firm’s clients. Although it describes the results as “market share,” Net Applications does not actually measure share of market in the traditional sense by revenue or unit sales. It does, however, provide a consistent methodology by which to measure operating system trends.

To see their July 1 report, click here. The results are summarized in the table below.

Drilling deeper into the numbers, ArsTechnica’s Charles Jade notes that the numbers for Intel Macs grew by a quarter of a percent to 5.26 percent, while PPC Mac’s declined to 2.7 percent. In other words, Intel Macs increased at twice the pace of decline for PPCs. “The rapid decline of PPC Macs coupled with sharp gains for Intel Macs no doubt factored into the decision to make Snow Leopard Intel only,” Jade speculates. His chart below:

UPDATE: Net Applications’ model must be more dynamic than we knew. At sunrise in New York on Monday, Mac’s June share was 7.95%. By 8:30 a.m. CT, when Jade posted his report, it had risen to 7.96%. By 3:00 a.m. ET Tuesday it had dropped to 7.94%. And these are last month’s numbers!

“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?