A big thing for me are the Macbook trackpads (and the standalone magic trackpads). They're just so awesome to use and no other manufacturer's comes close to Apple's.
In the last year I've gotten practically addicted to my Magic Trackpad. I've been using gestures on my MBP for a few years, but when I got the trackpad for my iMac at work last year and stated using it full time... wow.
If I want to play a game, I'll use a mouse. Same with drawing (or I'd get a tablet). But my my daily work of programming, surfing, email, etc the trackpad works great.
But the thing that has me addicted are the gestures. Three finger swipe left or right to go forward/back in Safari, IntelliJ, Mail, and every where else. Four fingers up to trigger Expose to show all my windows. Expand all fingers to show the desktop. Pinch-to-zoom is one I don't use much, but when you want to look at a larger version of a screenshot on a web page it comes in handy.
It seems like such a little thing, but I'm lost without the back/forward gestures. They are second nature to me now, and when I use someone else's computer I'm constantly frustrated by not being able to do it.
I'm sure there are gestures in other OSes at this point. Two-finger scrolling was an instant hit with me. After trying it, the PC laptop solution (special scroll areas on the trackpad) just seemed so pathetic. Two finger right-click was great. I'm still consistently surprised to see relatively new PCs with small trackpads. My boss has a 17" Alienware he bought last year, and it has a much smaller trackpad than the 5" pad on my 15" MBP.
