And one more yet... if you take a lot of screen grabs, consider
Skitch. It's a very nice program that provides really simple (but elegant) captioning, circling, arrow-pointing options. It also manages a library of grabs that you take, and it webpost them with a couple of button clicks so that you can post them in forums or inline them in a web page. It's great.
I occasionally still take opt-shift-3 screen grabs, because I want to capture something Skitch doesn't seem to handle correctly (like you can grab menu bars and things as full-screens with the keyboard, but you can't do it when you're using the mouse too, and so Skitch doesn't work well for that). I still just drag them into Skitch and delete the originals, though.
I can invite you if you'd like...PM an e-mail address.