Generally if a drive is going to fail, it usually will do so within the first few months. I've used 2 36 GB Raptors in one system (Raid 0) - they really should have, I'd almost say require, some form of active cooling. The case I used (Antec) had a spot for a front case fan in front of the drives.
Personally, I've had really bad luck recently with certain Western Digital drives. I'm up to 4 20 GB (WD204 model) drives and 2 40 GB (WD400) drives failed within between 3 days and 8 months of installation in the past 2 years. Two of the 20 GB drives were in the same computer, the first lasted 10 days (died on Christmas Eve), it's replacement lasted 8 months. I've haven't had one of their Special Edition drives die yet. I've also had good luck with the newer Seagate drives. Maxtor and Quantum are probably the worst brands IMO. They are even worse than IBM/Hitachi IMO.
(Just as an aside, most of the failures happened in systems owned by heavy smokers.)