I use a variety of OSs as and when required or needed. Currently on Windows 7 64-bit Pro, as I have no need to use anything else. It provides me with Visual Studio and general gaming.
I do however have experience with the following distros:
- Zenwalk Linux
- Ubuntu (and its variants, e.g. Xubuntu)
- BackTrack Linux
I suspect I'll be returning to linux very soon for work purposes, whether via VMs or dedicated setups.