there is a mingw port for windows. untested by me, but it looks credible. as for os x, that's all i use, and git works PAINLESSLY on it. i'm not sure where you got this information from.
Git works on OS X and Windows, but it isn't quite as fast (many of its speed optimizations are coupled with aspects of the Linux filesystem), and its maintainers are placing low priority on portability. I never said it didn't work, just that it isn't especially important to them. That raises a lot of red flags for me.
I work on amd64/i386/sparc OpenBSD at home and Windows at work, and I think version control systems are one of the tools that should be especially platform-independent: How will you port your project to another platform if you can't even track patches for it there?
I'm not saying that it doesn't work, just noting that so you can make an informed decision based on your priorities. I hear a lot of buzz about Git, but hardly anybody mentions this, and changing VC systems with thousands of commits can be extremely painful.
Where Git is written in a mix of C and sh scripts* , Mercurial is written in Python (except for a few parts written in C for speed, such as its diff algorithm), and its design seems far less coupled with any particular platform (and much cleaner overall, IMHO). I spent an afternoon importing a very large project (40,000+ commits, 10+ branches) currently using perforce into monotone, git, and mercurial repositories, and compared them. (This was on Windows.) The git interface seemed in many ways too rough around the edges to me, and while it was very nearly as fast as mercurial (and a bit faster than mtn, even with cached inodes), the database also needed to be re-compacted. Mercurial was much, much more straightforward to use than either mtn or git.
OK, I know you're probably not reading this anymore, but I'll give it a shot :-)
Could you give me a reference to "git is not quite as fast on OS X" because I certainly haven't noticed it. On windows I could feel how slow it was, but not on OS X.
