I like to be able to activate Exposé on my MacBook without moving my hand away from the trackpad. I figured I could do this by holding down the Command key while doing a secondary mouse click (i.e. a two-finger-tap on the trackpad), but couldn't find where to set this up in the Dashboard & Exposé System Preferences panel. The bottom section of the panel just showed 'Keyboard,' not 'Keyboard and Mouse.'
When I connected a USB mouse, however, the mouse shortcuts section appeared in the preference pane. I was able to set up the Command-secondary click shortcut, and it continues to work with the trackpad even after the USB mouse is disconnected. I really think Apple should enable this section of the preference pane on their notebook computers which are capable of a secondary click, even when no external mouse is connected.
[robg adds: On my PowerBook G4, the Mouse section shows up, even without a USB mouse connected. On my MacBook, it's not there. I believe the difference is SideTrack, which I have not yet installed on the MacBook. I'm guessing that the system sees SideTrack as an external mouse, hence, the Mouse shortcuts section shows up.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060718151422534