I got one of those cheap Pelican dance pads for my PS2 ($20). I don't have trouble with it "bunching up" on the floor like some people describe, but I did have trouble with two things:

1. The pad tended to rotate and creep off to one side as I used it.

2. I had a hard time telling where my feet were on the pad without looking down (since the pad pretty much feels flat all over). This is especially a problem when the pad has moved.

For #1, I got some of that carpet protecting runner from a home improvement store. It's clear plastic that's smooth on top, and spiked underneath. It's intended to protect your carpet in high-traffic areas. I got the kind for deep-pile carpet, since the spikes go deeper. I glued it, spiked side out, to the underside of the dance pad, using a hot glue gun (hot glue guns are cheap, you can buy them anywhere, and they're really handy to have for all kinds of things). I just glued it in strips along the dance pad. One thing I didn't consider is that it then prevents me from folding up the dance pad along the seams between the pressure pads (the plastic runner is too thick and stiff). If I did it again, I would cut the carpet runner into squares, and glue a seperate square under each pressure pad.

This helped the problem with the dance pad sliding and rotating, but didn't completely fix it (it just does it a lot less now).

For #2, I hot-glued a mouse pad to the middle square on the dance pad (on top). I used the thicker, spongey kind of mouse pad (mine's about a quarter inch thick) with the fabric-type surface facing up. This makes a huge difference in keeping track of where my feet are on the pad, since I can always feel the "home" position (kind of like those bumps on the F and J keys on a keyboard).