To finish off the soliloquy... effective mirroring with git
git-clone --bare git://host/repo.git mirror.git
git --git-dir=mirror.git config remote.origin.url git://host/repo.git
git --git-dir=mirror.git config remote.origin.fetch
'+refs/heads/*:refs/heads/*'
and now, on cron...
git --git-dir=mirror.git fetch -u
git --git-dir=mirror.git remote prune origin
(Thanks to Shawn Pearce for helping me figure out why it wasn't working for me!)
cheers
martin