the shuttle sn21g5 is available for purchase!

[Soymilk]

on paper, pros/cons are:

pros: g5 case, nvidia chipset, has pci-e x16 for graphics and a standard pci expansion slot

cons: uses the 6100/410 combo (lacks high-def integrated audio, although theres a pci slot so that doesnt matter that much; lacks gigabit ethernet, but thats mostly a gimmick; lacks dvi on the integrated video, but if you're a gamer you wont need that anyways)
g5 case can't take a double-slot cooler w/o some modding or leaving the top off the case

imo, most of the cons don't matter that much (unless you wanted this for a media center, then the dvi might matter more).

you can see dworley's take on it here: http://forums.sudhian.com/messageview.cfm?catid=43&threadid=90570&enterthread=y

summary of dworley's thread: performs on par with the evga matx sli mobo for gaming, if not a little better (his test rigs both had a 7900gtx 512 in em, but the evga mobo has a x2 4800+ while the sn21g5 has a x2 4200+).

3DMark06 - 5935 (SN21G5: X2 4200+ @2.4, 7900GTX 512 stock)
3DMark06 - 5963 (EVGA mATX: X2 4800+, 7900GTX 512 stock)
3DMark05 - 10546 (SN21G5: X2 4200+ @2.4, 7900GTX 512 stock)
3DMark05 - 10691(EVGA mATX: X2 4800+, 7900GTX 512 stock)

he overclocked to 220fsb stable, hasn't tried going further.