Why is Raid-Z better than Raid5?
"10 Reasons" that ZFS is worth it.
And from the FAQ:
Q: Can I boot my system by using ZFS?
A: The initial release of ZFS does not support a bootable root file system. This functionality is currently under development and will be available in a future release.
Q: Can I use a single disk with ZFS?
A: Yes. With a single disk, you can do one of the following:
* Use your disk as a single device, in which case you cannot benefit from the recovery capabilities provided by a ZFS mirrored or RAID-Z configuration, but will get the greatest capacity out of your device.
* Split your disk into multiple partitions and use them to build a ZFS mirrored or RAID-Z based pool. This options allows you to benefit from all of the ZFS recovery capabilities (unless your disk suffers a total failure), but you will have a smaller capacity in your storage pool.
Q: Can I use ZFS on USB storage devices?
A:Yes, provided that your USB device looks like a block storage device and can support an EFI label.
....Overall, ZFS functions as designed with SAN devices, but if you expose more simple devices to ZFS, you can better leverage all available features....
Interesting analysis of building your own Raid-Z fileserver.
The OpenSolaris forum also has a couple threads on building a NAS box here and here. But then there is also this OpenSolaris NAS Appliance page (and appliances in general).