If you're new to (or unsure of) CSS transforms at all, I can't think of a better explanatory introduction than this.
Plus, once again, Josh has managed to teach me some new tips and tricks about a topic I thought I had pretty well covered. In this case, the revelation of the (much cleaner, imo)
turn unit for rotational amount:
The turn unit represents how many turns the element should make. 1 turn is equal to 360 degrees.
It's obscure, but well-supported; the turn unit goes all the way back to IE 9!