I think it depends on the person. When my sister in law and I play hers always moves back. but the one I am using doesn't. We've tried moving her off the carpet and onto the tile. ... seemed to help, but hurts the feet.
Agree with the yoga mat suggestion, which works fairly well at keeping the pad stationary. That's what I do, and having been DDRing for nearly a year, I generally play the hardest songs on the hardest difficulties. Without the yoga mat within about a minute my pad is either pressed up against my TV unit with the arrows inches from my face and smushed up against the couch with the back arrow too bunched up to use :-).
I'm a heavy old guy and I actually like the thin cheap pad that comes with this game better than the expensive pads you can buy from other vendors. In the past I bought two pads from Red Octane for big bucks and both of them stopped working because my pounding seems to smash down the heavy padding and break the connective wiring. In contrast these thin pads when used on carpet are fairly comfortable and more durable than the the pads with thick foam inserts.
This game with an included pad is a steal at the price. And don't think you are too old, too fat or too slow for DDR. I'm over fifty and over 240 pounds and it's the most enjoyable workout I've ever had.
Your post was the inspiration for me to go ahead and get this, and I'm glad I did! I'm a few weeks shy of 50 and probably about your same size relative to height, and once I figured out how to shut off all the fancy schmancy stuff, I'm almost addicted to this! Not doing very well - yet - but I'm working on it and having fun.
Now if I could just figure out how to get that guy to SHUT THE HE77 UP while I'm dancing, I'd be happy! Can anyone tell me how to turn off the commentary while dancing? I'm working exclusively in workout mode for now, if that matters.
ya, i hate that condescending <insert chosen bad word>. grr. just step in rhythm with the music, really? big help chief. to shut him up (and it carries to all modes) go to the options menu in the main screen and you can either turn booing off (he's still a no-help poozer though) or turn him off all together (my fav).