Digging up an oldish thread.
IntelliPower is not variable RPM. It's WDC's way of saying they're not going to tell you what RPM the disk is running at, which will be somewhere between 5400-7200. As far as I know all models so far are either 5400 or 5900 RPM disks, although I don't have a break down which is more common.
Caviar Green and Caviar Black spec sheets say consumer RAID 0 and 1 have been tested and are supported with these drives. Anything else, all bets are off. Business critical RAID, the fine print on the spec sheet says are not recommended or warranted, and the consumer is directed to use enterprise class disks for such applications.
What's probably happening, is as John Murray described on Jan 31st. Consumer WDC drives do not have a feature called TLER enabled, and on at least Caviar green drives it can't be enabled, which allows for the disk to fast recover from disk errors, deferring error correction to a hardware RAID controller instead. When the disk attempts to use ECC to recover from errors, if this doesn't occur within the time the RAID controller expects (seconds) it considers the disk bad, and drops it from the array.
Software RAID 5, 6 as implemented by linux mdadm for example, will defer to the disk and thus isn't going to drop the disk from the array anywhere near as aggressively. Hence why some are having problems, and others aren't, in RAID configurations.http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701229.pdf