Here's a clever utility from the creator of Quicksilver. Secrets (no, not the Van Halen song) is a preference pane that lets you fiddle with the hidden defaults of nearly all your applications. For instance, show the iPhoto toobar in full screen mode and make those iTunes arrows link to your library instead of the store.
There's a huge database available, and adding your own secret preferences is simple. Have fun!
[Via Daring Fireball]