Keyboard shortcuts. Lot's of 'em. Even stuff from Classic like option-dragging the control strip to move it... All neatly compiled by Dave Polaschek.
I still have to tell people to use Ctrl-S on Windows to save. And every time I do I'm reminded of Kahn shouting that shortcut to a roomful of copy center PC users. My wife likes to learn as she goes. When she needs something done quicker, she'll ask me if there's a keyboard shortcut. I tried teaching her sevearl at once, she just got aggravated. So it's nice to see this gargantuan list in one place for our amusement. And as Einstein said, and I'm paraphrasing here, "why should I memorize something I can so easily get from a blog?"
And if you want to give your PC-lovin' friends a gift, tell them about the Ctrl-Enter thing in IE. They will thank you.