According to numbers released by IDC, income from server sales for Q2 2011 saw an increase of 47.5% compared to the same quarter 2010 to reach US$ 2.7 billon. This represented 20.5% of all income for the quarter. In comparison, income for Windows servers increased a healthy 12.4% to reach US$ 5.9 billion with represents 45.5% of all income for the quarter. These numbers in a very healthy quarter for all server segments.
If you get the calculater out of your pockets you will notice that GNU/Linux income increased by some US$ 870 million while Windows servers' incresed by some US$ 650 million.
In case you want to see the whole report, check here.