hmmm
I also mulled over this dilemma a couple months back, I ended up with a DNS 323 (and a $30 rebate that you can find at the official site) so it came out to be around 130 for me (no tax and free ship thanks to amazon)
It is quiet, can support 2 drives (not included), serve files to the PS3 (important for me), has bittorrent capabilities, has schedule download (I haven't use yet), USB for printer server that I can't/ don't have time to make it work yet and itunes server.
2 annoying things are the drives are not hotswap capable and that it has to be set up by the window based PC as far as I can tell... but the PC thing can be circumvented by opensource, I think. And once you map the drive and the network stabilizes, the macs would have no problem with recognizing it.
for a first timer with a whole afternoon free, the DNS 323 didn't make me want to knock my head against the wall (the DIR 655 did, but that's another story)
btw, it's not blazing fast, actually, the speed is about 2/3 of what I get from my sandisk USB, but I think my WD green drives contribute to some of that too.
oh, I just saw the Raid part, this NAS supports raid too. don't know for sure if it's hardware raid though.