Caution: I bought this drive at the end of last year and have so far been though 5 of these drives. The first one was DOA, and I've RMAd them four times when they stopped working. Each time, it was after a rare system powerdown, to change some cards. The machine came back up but the drive was inaccessible and wouldn't mount.
Last summer, WD posted a technote on their site saying to *never* pull the power plug out of the back of the drive because it could damage it (this is despite the fact that the user's guide says this is how you turn the drive off because it doesn't have an on/off switch). So before faiure #4 and #5 this summer and just 2 weeks ago, I followed this procedure and it didn't help. The last replacement (just 2 weeks ago) came with a new power supply and firewire cable and I also noticed that it's the Firewire+USB2 version of the drive and extended the warranty from 1 year (up this December) to 3 years. So I'm foolishly optimistic that this may finally be it and I can trust some data to this drive.
Anyway, if you do get this drive do *not* pull the plug out of the back to power it down.
As far as performance goes, it's fine. I used it for video editing and it was fast enough to capture 720x480 video in real time, but after the second failure I only use it for redundant backups of the stuff on my main drive. Good thing too. Fortunately, all I ever lost was digitized versions of analog tapes, so it wasn't too hard to redigitize them.