Print screen - only copies it to the clipboard? The Mac saves the file right there on your desktop.
I just *hate* that. 99% of the time the reason I am taking screenshots is to develop documentation. In other words, the screeshot is going to be immediately pasted into a document.
When it saves to the desktop, I then have to go find it, open it in some other program, select all, copy, change app, paste, go back to finder, delete file, go back to application, continue writing.
When it saves on the clipboard, I have to just click back to the other application, hit ctrl-v, and continue writing.