Hi,
I started GitExtensions about a week ago. Allthough version 0.6 is a pretty complete package, I do not consider it release-ready yet. The toolset should be ready for its first stable release in a few days. There are a few things I need to fix before anyone should use it in production. The most important problem now is that the shell extension part is written in c# and therefore can cause problems. I'm rewriting this in c++ at the moment, should just take another few hours. I also want to build in some features that should prevent users from screwing up (like create a stash ontop of another stash and throwing away work or commiting changes when in the middle of a merge). I allready finished allmost all git commands I ever use (push, pull, fetch, stash, branch, commit, merge, format-patch, am, apply, etc), so it should be usable pretty soon. The toolset is written in C# (.Net 3.5 until version 0.6, later versions use .Net 2.0) except the shell extension part. There is also a visual studio plugin, but this is still pretty basic.
I have not tried TortoiseGit yet btw, but I really like TortoiseSVN!
Henk