Git is usable on Windows - I've used it for the past year with cygwin. However my colleagues mostly switched to msysgit as they had issues with cygwin - msysgit looks like a better choice. Our server is on Linux though - I'm not sure how it will fare on Windows. We went through a few gotchas (crlf, case-insensitivity) but it was manageable.
Manageable is the most I can say though. I've come to the conclusion that going through the trouble of msysgit/cygwin is not worth it. I don't know if it's an option for you but have you considered other DVCS? From what I heard Mercurial is pretty good on Windows and you'd get pretty much the same advantages as with Git. Others might be able to tell you more about it.
I wouldn't go back to SVN on any platform though - I got addicted to local branches and the speed of having the whole repo locally.
Manageable is the most I can say though. I've come to the conclusion that going through the trouble of msysgit/cygwin is not worth it. I don't know if it's an option for you but have you considered other DVCS? From what I heard Mercurial is pretty good on Windows and you'd get pretty much the same advantages as with Git. Others might be able to tell you more about it.
I wouldn't go back to SVN on any platform though - I got addicted to local branches and the speed of having the whole repo locally.