I've tried it, but not on TC yet. The results for performance are the best I've seen yet for a over-the-network drive, probably due to the low level block access. (btw, it has to do a lot with scsi, it's "Internet scsi" after all)
For the target I used iscsitarget, and for the initiator I used open-iscsi and ms software initiator. The environment used had gigabit NICs and switches.
I ran into problems with sharing the resources as a SAN though (ie with more than one client), but didn't look into it much since I already had something else set up and working fine already (was just testing out this tech).