So I was over at the CocoaDev mailing list archive and and picked up this little tidbit.
Press the control key with the standard screen grab keys (cmd-shft-3 or cmd-shft-4), and the grab goes to the clipboard rather that the desktop. Quite handy if you do a lot of grabs. You also get a different sound -- more of a thwap! rather than a KaChink!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020501075139250