I used to turn on workout mode and play it until I hit 1000 calories. Doing that on a regular basis is indeed a workout, can't really do that with GH or RB.
I used to really love to watch my non-DDR friends trying to play. They'd never play much, though, since they sucked and I didn't. That's the thing, though, how the hell do you expect to get better if you don't try? I had one friend who was very seriously into martial arts, knew real ninjitsu-type crazy shit, he could do the stuff you see on youtube, yet he was just balls-awful at DDR. I was like c'mon, man, you should just try this for an hour, you'll learn it with your agility and footwork, but no. Every time he stepped onto the may, he would look like a wounded, drunk, dying rhino or something.
Then I swear to GOD, I'd play a song, be like, here, just do like this, then no. No, no, no, couldn't even begin to get the feel for it.
Weird how that skill doesn't translate to or carry over at all from anything else.