Often times, development teams like to discuss changes to the code base. This is mostly done through IRC (Freenode, for example), but I propose that bitbucket enables comments per commit, so developers can leave notes/discuss/yell about it.
The comments should be very simple, UI wise. Much like how facebook allows commenting on status updates – simple.
There should also be a counter, in the user's profile, for how many comments that user has made in all.