This hint is quite simple, but it's not explicit in Photo Booth.

If you want to take a photo and you're tired of waiting those annoying three seconds before the shot, just hold the Option key when clicking the red button. Alternatively, you can also use the Option-Command-T keyboard shortcut for the task! Pretty simple.

Even when shooting in this instant mode, there is still a delay between two shots -- try shooting several photos using the keyboard shortcut, and you always get the same image. It looks like the delay is caused by the "falling photo" animation. It would be good if someone finds out how to disable that animation.

[robg adds: Since the falling photo looke somewhat like a sheet, I tried using the NSWindowResizeTime trick (as explained in this hint) to speed up the animation. No go.]