Augie Fackler released a new version of hg-git yesterday, it should be relatively stable, there are still some rough edges, but it should be useable for most day-to-day tasks.
Please test it and report any bugs you find to http://github.com/schacon/hg-git/issues

If you have any questions or suggestions, or want to contribute to the development, there is a google group : http://groups.google.com/group/hg-git