We use git-svn extensively at work. It is pretty good at allowing us to keep our central core dev branch going on SVN with numerous teams not using git-svn, while allowing us to do all our release branching and such in git. I would not be happy to use it in a situation where we had multiple concurrent SVN branches, but then, I wouldn't care to be using SVN there either.

You really do get the bulk of the advantages; it's not perfect, and if you have to coordinate with someone not using git it can be a challenge, but it mostly works. People were briefly annoyed at our "patch bombs" but got over it.