I have had 4 of 4 WD 400 GB RE drives fail, all after the 3-year warranty.
I have 2 WD 5000YS drives (500 GB RE or RE2, not sure which) that are beginning to flake after 4+ years. I have 2 WD 5000ABYS drives (500 GB RE2) that are doing fine after 3 years. And I have 1 WD 500 GB RE3 (not ABYS, but not sure of the model name) that I bought recently to replace one of the 5000YS drives, and that is working fine.
All of these have resided (until failure) in an HTPC / video server (warm inside) running 24x7.
In my opinion, the 400 GB drives lasted long enough to be considered obsolete. By the time they failed, I could have replaced them all with two 1.5 TB drives running in RAID 1 instead of 4 in RAID 5, and the performance and reliability would have been similar, but with easier and faster RAID recovery, more storage, less heat, fewer parts, lower cost and less space in the case.