Just another data point, my git-svn clone of trunk comes in at 414MB, excluding the size of checked out files. I'm assuming the public svn is the complete history.
I'm about 35% through the process of cloning the entire gcc repository via git-svnimport, and the .git directory is 5.0GB. This includes all branches. Danny, which of these matches what you've done with mercurial? Ollie
