http://mail.google.com/support/bin/answer....amp;answer=6594
I never thought I'd be using them, but I went over them and now I use them all the time. It has become a habit. Sometimes, when I'm on my Hotmail or IPB PM Inbox, I accidentally press 'c' and nothing happens lol.
Also, Gmail recently made this hotkey thing that'll help IPB users select multiple PMs... click the first one, press SHIFT, click another one, and then every PM in-between will get selected. :D