I built a new PC last October (2011) using one of these as the primary boot drive.
All was fine, although I couldn't quite access all 2.5TB on a single partition due to BIOS restrictions on an older motherboard (2.2TB limit on Windows 7-64 bit).
After 4-5 months the disk errors started appearing, from random lockups and crashes mid application to later disk checks upon boot, with bad sectors, file fragments, etc and finally it refused to start. It wouldn't work connecting it to another machine via an adapter.
There seem to be quite a few complaints about the Caviar Green series, with possible issues about disk heads parking (load cycle) after seconds of inactivity, as a means to conserve power. For some users, this meant a lifetime of load cycles in a space of 6 months and quite a few failures.
I may have had an old one, as the drive I returned to WD was replaced (under RMA) with an identical model, but with revised firmware. Western Digital are quite good about this, taking about 7-10 days to get you a new drive, though you have to pay postage to send defective drives to them.
I'm currently using this as a backup disk and seeing how it fares in this capacity (note that you can't initialise a new disk using a USB adapter in Win 7, I had to use an eSATA port to do this).
I've since bought a 2TB WD Caviar Black for only a little more than this drive, which is slightly faster and hopefully doesn't suffer the fate of my original. If you just replace the hard drive and reinstall Windows 7, registration with the original product code is painless, much to my surprise.
The moral of this story - check the Load Cycle on the Caviar Green drives, check your firmware version, don't wipe copies of important data (keep them as backups), upload to skydrive/cloud, etc, and don't completely trust hardware; it's built to a minimal cost and will eventually fail.