How do you know it doesn't work? The pictures not showing up on the Desktop?
What troubleshooting steps have to taken?
What version of Mac OS X are you running?
Are you using any 3rd party screenshot apps?
I dosn't show up on the desktop but it seems to take the picture, i got macbook 13 inch aluminium leopard.
And the only thing im doing is pressing Cmd shift 4 or 3 holding down ctrl dosn't work either