I've had some pretty bad experiences with WD, all the way back to their 1.6GB drives that always failed, but one person really can't judge the reliability of a manufacturer as a whole. You have to look at the overall picture. For example, look at NewEgg and you'll see a much higher percentage of complaints on WD drives than Seagate, but WD is still doing well overall.
The most important thing to me as far as reliability is warranty and RMA policy. With any drive, it probably won't fail, but if it does fail you want it to be covered and you don't want to be hassled.
Seagate and WD both have good RMA policies every time I've had a drive fail. Maxtor and Hitachi/IBM do not. They both give you a really hard time. Maxtor and IBM used to cross-ship drives. They don't anymore. You have to send in your old drive and wait a few weeks before they'll send out a new one. Hitachi will harrass you quite a bit, telling you that you need to run their diagnostic software and get a code from it, and if the drive has bad sectors they'll just tell you to low-level format it then run the program again (which will tell you there are no problems even when there are). It's really ridiculous.
So, Hitachi makes fast drives, but I'm never getting another one. I'm sticking with Seagate and WD (and maybe Samsung). Right now I think the Seagate 7200.8's are the way to go if you're not getting a Raptor 74.