The newest Abit boards based on the 865 and 875 chipsets definetely have memory incompatibility problems. I have built 5 computers for friends and family this month. 3 of those computers had Abit boards, 1 - IC7 and 2 - IS7. I had problems with all the Abit boards.
On the other hand, I have never had a problem with the P4P800. I have one, installed one for my dad, and installed one for my brother. They all work flawlessly.