I've interviewed at a couple local companies with 50+ devs each (mostly web dev positions), and almost everyone uses a Mac. This is anecdote of course, but I very rarely see devs using Linux professionally (natively, not in a VM).

That said, it depends on the kind of work; obviously, .NET developers almost exclusively use Windows, and I've noticed that sysadmins and system engineers are a little more likely to use Linux.