The percentage of Web users running Linux devices passed the 1% mark for the first time last month, thanks in part to increasing acceptance by mainstream PC vendors.

According to Web metrics firm Net Applications, the usage share of Linux on client devices reached 1.02% in April.

"Linux has been successful primarily as a server operating system, but client usage share has not kept pace with server share," the company said in its report. "Linux has reached this important milestone on the client as Linux-based systems have become more functional, easier to use, and preinstalled on computers from vendors like Dell."

Since the emergence of graphic interfaces for Linux like KDE and Gnome in the late 1990s, Linux supporters have speculated about when and whether mainstream adoption might be seen. Though now common in corporate data centers and popular among the tech savvy, Linux remains inconsequential to most consumers, despite the innovations it has enabled through companies like Google that rely on it.

Microsoft Windows is still the dominant operating system around the world, but among Web users its global market share is showing signs of weakness. In June 2008, 90.84% of Web users ran Windows. In April 2009, Windows' market share, at least as measured by Net Applications, had declined almost 3 percentage points to 87.90%.

Apple's Mac OS X appears to be the greatest beneficiary of this trend, having seen its global market share among Web users rise from 7.94% to 9.73% during the same period. This does not count rising usage of iPhones and iPod Touches -- both of which rely on a version of Mac OS X -- pegged at 0.16% and 0.04%, respectively, last June and at 0.55% and 0.15% last month.

The news isn't all good for Apple, however: Its Safari browser saw its global market share drop slightly, from 8.23% in March 2009 to 8.21% in April.

In any event, Linux seems to have gained at the expense of Windows, too. It had a global market share among Web users of 0.80% last June. Having reached 1.02% in April, its growth rate is slightly higher than that of Mac OS X.

Windows' slipping market share may be because of a variety of factors, including the popularity of netbooks running free software, lackluster adoption of Windows Vista, security worries, and effective marketing from the competition. It's clearly a trend that Microsoft hopes to reverse following the release of Windows 7 later this year.

InformationWeek has published an in-depth report on Windows 7. Download the report here (registration required).