I have increasingly been using virtual machines for my Tor activities. Actually, I exclusively use VMs now that that we've seen deanonymizing server-supplied exploits in the wild. I install an operating system in VirtualBox and immediately export it as an appliance. I do this for several operating systems: WinXP, Win7, and a few Linux distributions. That way I have clean images that I can re-import if I suspect something bad has happened to one of my VMs, like it was infected with malware. It's easier than reinstalling an OS on the whole computer, and you can isolate Tor from the browser by putting them in separate VMs, making it much harder for an exploit to get your real IP address. You can also store sensitive files outside of the VM that you browse in, so exploits can't access them.