For both joining and leaving would be good, and also notification in a chat window with them if you have one open.
And being able to select a custom beep noise (for all beeps, possibly not on a per-notification basis). I'm personally a fan of the processComplete sound.
Also perhaps you could do a list of perms with a "Any-Build-Full-Friendsonly" selection (four checkboxes and all to the left of the selection are implied) for things like who can see your online status, send you messages, send you server invites, see where you're connected, and the like.
ie
Permission Any Build Full Friends
See Online [x] [ ] [ ] [ ]
See Connected [x] [x] [ ] [ ]
Message [x] [x] [x] [x]
Invite [x] [x] [x] [x]