We have been using the Tyan Thunder S2882GNR-D Motherboard and AMD Opteron 270's and Chenbro Chassis with much success since the Supermicro stuff looks like Intel is holding sway... With the Zippy brand power supplied, LSI-Logic RAID 2x, broadcomm NICs, Crucial memory, and Fujitsu Ultra320 SCSI disks we see very little breakage, like none, on the app cluster.
Those older AMD chipset boards are solid are not they? I installed a dual Opteron 242 box with 2GB of RAM (4x512MB) using the 2881 board I was talking about. This was about two years ago. A 3ware 7508 + 6 200GB IDE disks + 2 scsi disks as the system disks + 350 watt redundant, ATX sized, 2themax power supply :D. I never got a complaint about its stability.
Another Tyan box that is relatively new that (Tyan 2865) I built (but running Windows XP 64-bit) has also been rock solid once I replaced the incredibly expensive and incredibly unstable 3dlabs Wildcat Realizm 500 with an elcheapo ATI card. If I had known that 3dlabs was leaving the market...
So if Tyan is losing its edge with its new stuff...that is a real pity.