Our entire development team uses Macbooks - and of 12 users, only two of them run OSX. One of them is even geeky enough to paste a Tux logo over the light-up Apple logo.
The last time I visited Google HQ (about 5 years ago) the most common setup I saw was Thinkpads running Linux with Macbooks running Linux in a close second.
"I go on working for the same reason a hen goes on laying eggs." - H. L. Mencken