I did keep my PS2 to continue playing games like Guitar Hero and to cover my butt in the event a game I have doesn't work (the fact that you can now transfer PSX/PS2 saves from you PS3 to a PSX/PS2 memory card helps with this). I've yet to encounter a game that doesn't work on my PS3, but like I said, I have one with the emotion engine built in. Keeping old systems is never a bad idea anyway, and if you needed to get one, a new PS2 is quite cheap anyway.