I've used WD for over 10 years and wouldn't use anything else (internals). I've had one external drive, and despite being in an enclosed aluminum case with no fan, it still runs daily for several years now without a problem.
I have Buffalo Linkstation Duo NAS, brand recommended by VanB I believe (or maybe Wolf). Paid something like $240 or so, 2x500GB hitachi drives (of course nowhere can you find the HDD brand they used, I had to open it up). Bought it summer of '09 and aside from a little fan noise occasionally, it's been great. However, the USB (for attaching additional external drive) sucks. The access speed was way too slow, but the gigabit lan was pretty good. Been running it in Raid 1 and no problems.
I primarily use it as a music server with a shared iTunes list, or the DNLA media server. I think it has a bittorrent feature too.
"You're not going crazy. You're going sane in a crazy world!" ~Tick