After showing impressive gains in December and January, Mac OS X’s slice shrank a bit last month in the latest Net Applications survey of operating system market share. The iPhone’s share growth, meanwhile, continues to outpace every other category except “Other.”

As Net Applications measures it (more on its quirky methodology below), the Mac’s market share dipped to 7.46 percent, 1.45 percent off its January record high. Apple’s AAPL iPhone, meanwhile, hit 0.15 percent, a personal best, up 7.69 percent from January.

Microsoft MSFT Windows in all its flavors continues to dominate, with a 91.58 percent share, up a hair for the month but still off the 93.3 percent it held a year ago.

Net Applications’ monthly surveys sample data from visitors to some 40,000 websites operated by the firm’s clients. As such, the findings are a snapshot of installed base — with a bias toward machines that spend a lot of time on the Net — rather than a month-to-month measure of computer systems sold. The February results are summarized in the table below. The full report can be viewed here.