Really? Bugzilla? Talking about bad user interfaces. Anyway I don't see the BitBucket guys integrating Bugzilla anytime soon since they're part of Atlassian now which markets the Jira issue tracker.
Nope - I'm not really talking about Bugzilla or Jira from a UI point of view, but more of a functionality angle.
That's the thing - the UI for issue tracking, on both Github and Bitbucket, is great. No functionality however.