We have it and it is a lot of fun. The kids are really good at it. If you get the Xbox version and you have Xbox Live, you can play it online and you can also download (for a cost) extra songs. I think it's 5 songs for $5.00 and I believe there are like 5 downloads, but I wouldn't swear to that. My kids could answer that more than I could. If you're interested, I can ask them when they get home and post back later.
I remember reading one of your posts at one time where your family was having this really good tasting dinner and I remember you were having a weight watcher's meal? Maybe I'm wrong with my memory, but in case I'm not, I wanted to add that I saw a lady (and I cannot remember which channel it was on) on TV who said she lost over 100 pounds just playing this game.
Trust me, it will give you a workout, but it's a fun one. I highly recommend it for that reason alone.
Oh, I only have the one pad for it. It came in the package for either $70 or $80 at Circuit City. I'd like to someday pick another mat up, but I feel we use it, but maybe not enough to buy another mat.
Another thing, this afternoon, I got a free Playstation Underground magazine. They send them to me from time to time and there is something about a new DDR on PS2. I'm not sure if it's a playable demo, a movie about it or what it is. It might be worth checking out.
edited to add: Go to your local arcade, usually the ones in the malls have this game. Watch the kids sometime. They love it!