How about a warning for Mac users to not get too complacent with their sacred shortcuts?
ie. no option drag to copy or click drag to highlight [sniff].
As for really useful ones (on Mac, anyway):
1. zoom to selection = command / pageup
2. zoom track height to full window = shift / tilde (~)
3. go to start of project = home
4. Spacebar = play. (just kidding)