I am reading the CAVEATS of git-svn. via this SO question.
What I understand is that:
If you are mirroring svn trunk, branches etc on git repo, don\'t merge
git-svn is crippled by definition. You can't do anything Subversion doesn't grok, like merges.
HOWEVER, you can bend around Subversion's rules temporarily with rebasing. I've shown an example of this in a blog-post/screencast:
http://blog.tfnico.com/2010/10/gitsvn-4-collaborate-with-other-git.html
(Lots of more tips on working with git-svn here.)