The monthly data from Net Applications was released today – yes, New Year’s Day – and it shows that the Mac has eked out another incremental gain in share.

California-based Net Applications doesn’t measure market share by units sold, as do other research companies, but by sampling traffic data from its client Web sites.

For December the Mac’s share of Internet traffic was 7.31 percent, up from 6.8 percent in November. An incremental gain, but if you look at where the Mac’s share was in December 2006 – 5.67 percent – you can see the results of a steady upward trend throughout 2007. If you go back to January 2006 (the earliest data available on Net Application’s Web site), the Mac had only a 4.21 percent share.

That’s a major leap for the Mac platform, and jibes with traditional market share data from research firms Gartner, which put the Mac’s U.S. share at 8.1 percent in October and IDC, which put it at 6.3 percent. As with the Net Applications data, both numbers were increases from previous reports.

(The iPhone, by the way, shows up in the Net Applications report with a share of 0.12 percent, up from 0.09 percent in November and 0.07 percent in October. Watch for iPhone share of Web traffic to shoot upward in 2008 and beyond.)

Almost every measure of market share in 2007 has shown the Mac gaining. If 2008 proves as good to the Mac as was 2007, we could see reports by the end of the year that show Mac market share in double digits.