http://en.wikipedia.org/wiki/Linux_adoption
"In 2009 Microsoft CEO Steve Ballmer indicated that Linux had a greater desktop market share than Mac, stating that in recent years Linux had "certainly increased its share somewhat". Just under a third of all Dell netbook sales in 2009 had Linux installed.[51]
Caitlyn Martin, researching retail market numbers in the summer of 2010 also concluded that the traditional numbers mentioned for Linux desktop adoption were far too low:
It seems like almost every day someone in the tech press or someone commenting in a technical forum will claim that Linux adoption on the desktop (including laptops) is insignificant. The number that is thrown around is 1%. These claims are even repeated by some who advocate for Linux adoption. Both the idea that Linux market share on the desktop is insignificant and the 1% figure are simply false and have been for many years...Where does the 1% number come from? There are two sources: very old data and web counters. The problem with using web counters to try and ascertain market share is that they generally only include websites that have paid to be counted. That pretty much guarantees that Windows will be overcounted.
—Caitlyn Martin[51]"
this means linux do have ~10% market share on the desktop