I find myself using the following often to get a limited number of revisions out of our huge subversion tree (we're soon reaching svn revision 35000).
# checkout a specific revisiongit svn clone -r N svn://some/repo/branch/some-branch# enter it and get all commits since revision 'N'cd some-branchgit svn rebase
And a good way to find out where a branch started is to do a svn log
it and find the first one on the branch (the last one listed when doing):
svn log --stop-on-copy svn://some/repo/branch/some-branch
So far I have not really found the hassle worth it in tracking all branches. It takes too much time to clone and svn and git don't work together as good as I would like. I tend to create patch files and apply them on the git clone of another svn branch.