It's very easy to take a screenshot on the Mac with either Command-Shift-3 or Command-Shift-4, and they will be dumped on your desktop. One major annoyance, however, is that the files created have no extension.
That may not be a problem on the Mac, but when you're trying to email these files to Windows users, they cause problems.
So the question is -- how can I force the Mac to save the screenshots with the .png extension? Thanks.