I hate to say it, but my main PC runs Windows 7. I just don’t have time to maintain a Linux system when I’m doing critical work.
My other 2 laptops however do run Linux. I’m running Ubuntu at the moment for the same reason as above, because I’m lazy!
As for servers, I run a combination of Debian and Gentoo depending on what I’m planning to do, and if its a server I want to play with, or seriously use in production. The server running this blog is Debian.
I’ve also done some dabbling in Mac OS X, but I don’t have a laptop (notice the laptop theme) thats powerful enough to run it, apart from my main one (no I’m not going to buy an actual MacBook!)