I selected a smart playlist today in iTunes, and without thinking about it, instinctively hit command-I. Presto, the Smart Playlist editing box appeared!
[robg adds: OK, this shortcut is documented, in the sense that File: Get Info is active with a Smart Playlist selected. But I would never have guessed it would show the edit dialog, so perhaps others have missed it as well. This is a nice keyboard-only solution to quickly editing Smart Playlists (I've been using Option-double-click).]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060208204820272