A mailing list for when Facebook deploys changes to their sharing buttons/features would be extremely useful. Sometimes the changes made by Facebook alters the performance of our site and I would like to run tests when changes are made.
http://developers.facebook.com/support/community/ it isn't a mailing list per se, but there's a number of ways there for you to keep up to date on FB tech happenings.
Cheers!
Cynthia