I made myself a little command-line tool gravatar.rb today, which eats email addresses and outputs "gravatar-url email@address" lines, for all email addresses that has a customized gravatar created.

It's fun to run git log|gravatar for projects you've got checked out; here's yui3:

(People showing up more than once either have multiple email addresses registered with gravatar that they commit via or borrow someone else's picture. :-)