One pretty awesomely simple thing under Mac OS is making great screenshots.
You might already be familiar with Mac OS X’s classical shortcuts for screenshots, Shift+Cmd+3 (full screen) and Shift+Cmd+4 (selection). But did you know you can shoot a single window without the hassle of selecting it from edge to edge, or worse, cropping from a full screenshot?
Press Shift+Cmd+4, then press the space bar.
A little camera appears, and allows you to capture the highlighted window of your choice.
The resulting image can be found at the same place as usual screenshots – by default, on the desktop, as a PNG file. With transparency and drop shadows, nothing less!
NB: apart from “real windows”, this camera can also capture the Dock, the menu bar, the desktop wallpaper, and even widgets.