I've had my 60D for about three years now, and still don't feel any compelling need to upgrade. It's capable of more than I am aware and I am still learning about some of its features. As mentioned above, the tilt/swivel LCD was a big feature for me too. I had gotten spoiled by that feature on my Canon G5 and held off on getting a DSLR until I could get one with the same type screen. A big help for low angle and overhead shooting and great for protecting the LCD when not in use.
Recently bought a Yongnou YN565EX flash and it can be set as a slave and fired wirelessly with the 60D. That's another one of those features I'm just now growing into that didn't seem so important when I bought the camera. Here's a couple shots from my first outing with the new flash, just mounted on the camera hot-shoe and bounced off a white ceiling.