We just switched over to an Xsan from an Xserve RAID. With the RAID I had some problems, mostly with dropped frames during digitization (SDI, Dual 2G G5, etc.) and inconsistent insert edits with ETT (which may have been FCP 4.5 related). Initially, we had severe sync issues that traced back to the RAID, and toward the end I had to digitize all my 10-bit stuff to a local drive and then transfer it. The RAID wouldn’t allow any 10-bit material to import without dropping frames or stalling the batch capture. It may have been solvable, but once you’ve got 600GB of stuff already on it it’s a little diffiicult to troubleshoot without losing it all. So, since we we’re expanding anyway, we just set up an Xsan network and sold the RAID.
Judging from what everyone else has said about the Xserve, I think mine might have been cursed.