I took the plunge with the iOmega Netstore 2TB model. It's two 1TB drives that's configured in RAID 1. The setup was reasonably painless. It's supposed to be easily upgradeable (switch the public drive out with a larger drive and copy the backup drive onto it).
I felt for the price ($229US) it was a great value for me. I have one desktop and 3-4 laptops/netbooks using the network in my home at any time. Before the NAS setup, the fasmily's iTunes library was shared from the desktop. Now its on the NAS and I have the drive backed up along with backups of my computers as well.
It also has the feature to turn off the drives when we are at work or asleep.
Annecdotally, my electric bill has gone down $6-8 per month compared to before the NAS was installed and the desktop was on more often, so I'm in the get a NAS camp