Xsan 2 has been received some significant updates; not only is it now fully compatible with both OS X Leopard and OS X Server Leopard (in fact, Leopard is required to run Xsan 2), it is also now qualified to work with third-party RAID storage.
Even more exciting (at least for anyone who has been holding out for some kind of Final Cut server solution) is the introduction of what Apple is calling, MultiSAN. MultiSAN, according to Apple, "[allows] users on a single workstation to access multiple SANs at the same time." Using the video editing example, this means that a segment producer could access both a broadcast and b-roll volume from the same machine. Additionally, the administration tools have been redesigned. Administrators can now create pre-set volume workload settings for different file types/purposes.
To be clear, this is an enterprise product. Xsan 2 is available now for $999 US. Xsan 2 is qualified to work with the Xserve, Mac® Pro and Apple Fibre Channel PCI-X cards, as well as qualified Fibre Channel switches and RAID storage hardware from third-party vendors.
Update: As Tim in the comments pointed out, it appears that Apple's Xserve RAID device is no more. The page now re-directs here, with a link to Promise's RAID solution.