I haven't seen anyone mention the Intel version of Tiger server yet, so I will. I received a Mac Pro last week, having ordered it hours after the announcement. Its being used as a workgroup server for the university I work at. I hooked it up to our Xserve RAID via a Qlogic 1400 fibre channel switch with the built-to-order apple fibre channel card (LSI model LSI7202EP). So far I've set it up for AFP sharing, NFS and Netboot and everything seems to be working well!!
The PCIe fibre channel card seems to be of the 4Gbps variety, unlike the PCI-X card which is 2Gbps.
Some build information for Tiger Server x86:
System Version: Mac OS X Server 10.4.7 (8K1079)
Kernel Version: Darwin 8.7.2 Tue Jul 25 23:09:54 PDT 2006
It's SOOOO much faster than our old server. Its replacing a G4 400Mhz (PCI Graphics). I wanted to replace it in early 2005, but then apple announced the intel switch. I wasn't about to buy a G5 tower or xserve, so I waited patiently and it was worth it. Making netboot images with netrestore doesn't take all day anymore!!