Gamestop and EB Games is offering $100 off the purchase of a PS3 by handing over your PS2. The PS3 does play PS2 games, albeit a little jagged, so getting $100 off for trading it in could be construed as a good deal -- especially if you're part of the PS2 sporadic "disc read error" crew. This advertisement and deal is one the first true signs that retailers have stock and want those systems out the door.
We now wait to see if any other retailers begin offering deals to move PS3s. Stores aren't making very much money off of the systems, so moving those puppies out is top priority. The real profit exists in getting customers to buy games and accessories.
So, while the retailer gets rid of their stacks of immovable PS3 consoles with this deal, they also get your old friend who certainly will sell. This deal means Gamestop gets your $400 - $500 from the PS3 purchase, plus whatever accessories and games go with the sale, and then they will sell the traded-in PS2 for another $100 to someone not ready to upgrade. Ding, they break even or profit, and everyone walks away happy.