Just ordered a bunch of parts to explore iSCSI SAN in more detail. At this point it looks like Monday will be the delivery date. Major components being Supermicro Atom D510 based ITX motherboard with dual Intel Gigabit NICs, Highpoint Rocketraid 2710 (SAS 6Gbps 8 port), and 4 seagate 2.5" drives.
Been testing out Openfiler and Nexenta at work on some old hardware that's not being used. On a dual core dual socket Opteron 270HE with 8GB memory, Areca ARC-1120 and 8xSeagate ES drives, they can hit some pretty impressive numbers. However, it seems that Nexenta's use of Opensolaris is superior possibly due to a better implemented iSCSI target software.
Nexenta seems to be more polished and mature despite some hiccups seen in the WebGUI and in general performs better and more consistent with very low CPU usage. If you are a business, Nexenta is the way to go with the option of block level replication and active/active redundancy. Now if you are a home/small-business user, take a look at www.nexenta.org for the free version with 12TB limit. An other option that I've yet to explore is EON ZFS Storage. It looks very promissing and comparable to that of Nexenta but is opensource and has no limits.