No, I'm serious. I got one from SchmilK's mom and used it on my bathtub a couple of weeks ago. We have one of those textured plastic tubs that collect black gunk and no amount of scrubbing or bleaching gets rid of the black film... well I used the sponge thingy and it was like swoosh swoosh immaculate. I used it on scuffs on the walls as well and to clean the black soot out of candle holders.
When I had the mattress business I'd use cut up pieces of foam for the same stuff, so I think that's basically all it is, it works the same way.