I already use umpteen HDDs as backup and have a twin drive Mac - SSD for the OS and 'daily' files and an HDD for initial backup.

From what I understand from Marcos' thread on the Pi the real benefit is using a NAS array is so your songs are readily accessible throughout the house. As I understand it the NAS takes the form of a twin drive RAID where you can dump all your tunes (and more) - the only drawback being that this would require backup unless the raid is 'self healing' which is not the case according to Neal's points. So the issue for me is that not only would I need a networkable RAID (i.e. not USB) but also a second drive set for backup of equal size.

This makes the whole 'cheap as chips' philosophy of the Pi pretty much redundant - it wouldn't really add any real benefits above what I already have but would simply cost a fair smack.

Or am I missing something?