I called them 3 years after buying RAM for an iMac, because I was getting an an error in OSX that Apple said was bad RAM. No hassles, no problems, they cross shipped the RAM and I had it the next day. Their prices aren't that much more than generic RAM, the warrenty and service are unbeatable, they ship quickly, and I've never had a problem with Crucial's configurator giving me the wrong answer (ehem, Kingston, Viking).
Given the choice I wouldn't buy anywhere else. The only time I've had to was with a PC that needed RDRAM which Crucial doesn't sell and it was a nightmare to get the correct thing (ehem, Kingston, Viking).