Okay, not so hot.
Since I converted to Macs (about 4 years ago), I find that whenever I discover a shortcut or hot key that I didn't know about I feel like I found a miniature hidden treasure. Here are some of my favorite recent finds:
ctrl + eject = shutdown the computer.
It still asks you if you are sure, but at the end of the day, anything that makes your egress faster is truly a HOTTkey.
shift + volume = adjust volume without the chirp.
If you are ever presenting something and you want to make an adjustment, this makes you feel like 3% cooler that you don't have to listen to the volume chirp. Also nice when you have headphones on.
Command + K = connect to another computer. With the new OS it's not as fast, but if you are working with a bunch of other macs this makes things a lot faster.
Command + Q = quit application
Sorry this one is not new, but probably one of the most satisfying hot keys.