I'm having a similar problem with this same board. I recently added a second 8800GTX in sli and at idle I'm seeing temps of 57c!! I tried out Crysis and while it runs extremely smooth and stable I saw temps up to 70c on the mobo! I called Asus and one guy told me I should see temps between 30c-50c for this board, while another guy told me I should see temps between 45c - 65c. Who do we believe?
All other components are running extremely cool except the mobo, even the GPUs. The only thing I can gather is that either the second pci express slot is covering the south bridge creating the extreme heat, or the probe is very close to the bottom pci express slot and the probe is just getting the temps off the second GPU. I've been trying to figure out a solution of how to keep it cool.
Here are my specs. I'm not overclocking either.
AMD 5600
M2N32 - Sli Deluxe Wireless Edition
Asus 8800GTX x2
4gigs Corsair Ram
WD 150gb Raptor
WD 250gb 7200 x2 Raid 1
850watt psu
2 exhaust fans (1 rear & 1 top), 3 intakes (1 front, 2 side hitting RAM and top GPU).