If you buy your books at Amazon and not at Buy.com you should be shot. Buy.com guarantees to beat Amazon by 10%.
As for other stuff, they're usually ok.
Service is ehhh. No phone # to call. I once bought HL2 Collectors Edition during a crazy sale where itw as $28. I shipped it to the wrong address and they didn't respond in time that Fedex shipped the HL2 back to them. THe only way for me to get it was to reorder. I blamed them for being too slow to contact Fedex to fix the address. As a result, the HL2 deal was over and itw as like $80... I had to settle for a Fry's $19.99 deal later on, but that was just regular HL2, no collectors dvd version.. =(