Windows still dominates, but alternatives are gaining ground on both clients and servers.



From PC World:

What's particularly interesting, though, is the rapid growth being shown by both Linux and Macs in the server and client operating system segments, respectively.

On the client side, for instance--which as a whole grew 9.3 percent in 2010--Mac OS was the fastest-growing subsegment in 2010, even though Windows was still the largest client OS player. Apple's platform grew 15.8 percent to $520 million in 2010, fueled by what Gartner reports were strong sales of Mac desktops and laptops.

  Linux and Mac OS Are Fastest-Growing Operating Systems