Mac hits record 7.8% market share in Net Applications survey

After drifting inexplicably in February, March and April — actually losing market share in two out of three months just when Macintosh sales seemed to be on fire — Mac OS X recovered smartly in the Net Applications survey issued overnight Sunday.

Apple’s (AAPL) share of the operating system market grew 5.69% in May to hit a record 7.80%, while Windows in all its flavors dropped half a point to 91.17%. That’s a record low for Microsoft (MSFT), which nonetheless still runs on 9 out of 10 computers on the Internet, as Net Applications measures it (more on its methodology below).

The iPhone’s OS market share, whch Net Applications measures separately from OS X, has temporarily leveled off, according to the report, reflecting the shortage of product as Apple cleared inventory in May and customers held off purchases in anticipation of the new 3G model. In an IDC report issued Friday, the iPhone actually lost share in the smartphone market, falling from 26.7% in the last quarter of 2007 to 19.2% in the first quarter of 2008. RIM (RIMM), meanwhile, gained share in the same period, growing from 35.1% to 44.5% on the strength of new, consumer-oriented BlackBerries.

The discrepancy between IDC’s and NetApplication’s numbers can be explained to some extent by the nature of the two surveys. IDC’s quarterly reports are sales counts, based on surveys of retail outlets. Net Applications, by contrast, collects data from the browsers of visitors — some 160 million per month — to its customers websites. As such, its findings are probably better described as a snapshot of installed base taken from a less-than-random sample. But the results are useful for indicating trends, and tend to correspond well to domestic market share as measured by more traditional methods.