They may be quiet/inexpensive, but they also don't ship with Time-Limited Error Recovery enabled (http://en.wikipedia.org/wiki/Time-Limited_Error_Recovery). This makes it much more likely they'll drop out of an array. Some models can have this option flipped on; some cannot.
I installed two Caviar Black (b/c of the 5-yr warranty) drives in a RAID array a few months ago. The RAID edition drives aren't even significantly more expensive. I wish I'd known this earlier.
This is a bummer. http://wdc.custhelp.com/app/answers/detail/a_id/1397/p/227,2...
Edit: But on another page, WD says that Caviar drives can be used in consumer RAID configs. Hmm. http://wdc.custhelp.com/app/answers/detail/a_id/996/related/...