There's a mirror at
https://github.com/mirror/calibre for users that prefer GitHub (originally mentioned at
https://bugs.launchpad.net/calibre/+bug/1093634).
The mirror has pull requests that it would be beneficial to discuss within a reasonable time because the possibility of merge conflicts increase with time.
The pull requests can be applied with
*`bzr git-apply`
* or by asking me to upload to launchpad with `git bzr push`