Well, my interesting note is that Vista is more stable than Linux. Specifically, the C2Q9450 on an MSI X48c Platinum with 2GB OCZ low latency DDR3 would lock up frequently - at least daily - when running the SMP Folding client on Ubuntu. So far it has been rock-solid stable on Vista Ultimate with 4 single-core Folding instances running. In fact, under Linux I couldn't OC the rig at all and even had to slow the LL RAM to more normal speeds. Under Vista I'm now slightly OCing the machine.
I've actually just ordered Windows Home Server & the
1.5TB Seagate and will re-do the machine as my AV server & workstation backup platform. I'll eventually add dual 4870s if the price comes down for extra Folding goodness.
The rest of my farm is pretty pedestrian: 4 Q6600s (3xVista, 1xXP; 1x4GB, 3x2GB, 3x HD3870; 3x500GB Samsung, 1x80GB Fujitsu notebook drive) with no serious overclocking, 1 C2D T7800, and a lowly 2GHz P4M. Not all are on 24x7 and during the hieght of summer I powered most of it down to cut the electric bill. A lot of it is in my basement where the heat & noise aren't an issue; with cold weather approaching I may distribute them around the house in rooms we don't use much to take advantage of the generated heat. Partially offset the electricity with reduced natural gas consumption.
I'm sure I could have higher PPD if I tried and did some OCing or other workarounds, but it is fine for the moment. It's easier to throw a few $ at it than find the time & desire to tinker.