Gravatars stops being displayed on Bitbucket, if only they have rating any higher than
G (general). This is way to tough, in my opinion. You should consider allowing at least
PG (parental guidance) rated gravatars.
gravatar.com's definition for
PG is: "PG rated gravatars may contain rude gestures, provocatively dressed individuals, the lesser swear words, or mild violence". That isn't to high, as for developers, right? :]
I don't know, if this is valuable, but as my supporting argument, I say, that entire Stack Exchange network (quite very similar to Butbucket, at least in terms of target audience -- developers) allows gravatars rated at
PG and only blocks
X rated ones.