Apple released Thunderbolt Mac mini Servers today, with Lion Server preinstalled (which now includes Xsan). Standard kit is a quad core 2.0 GHz Core i7 CPU with dual 7,200 RPM 500 GB HDDs and 4 GB of RAM. BTO options include dual 256 GB SSDs with TRIM support, and up to 8 GB RAM.
Unsurprisingly, the Gigabit Ethernet on board no longer claims jumbo frame support (no Core iX Mac thus far as supported jumbo frames on its built-in Gig-E NIC).
85 Watts. That's it. Near silent operation, trivial heat output. Now we just need Promise to ship SANlink.
Bone stock list price is $999, fully loaded hardware (8 GB RAM and dual SSD options added) lists for $2,199.