I had the same problem with my 2 bfg 9800gx2.
quad-sli disabled -> worked fine
quad-sli enabled -> freeze after freeze.

have a look at ur nforce driver, asus delivered mine with a very very old nforce driver.
my system is stable without freezes since i updated the nforce driver.
and well...don't waste ur timing at asus forums or support. i like my asus boards but support and forum just suxx.

hum...the pinotnoir...i like the pcb, but the wc wasn't even able to cool the board xD