I am running an Athlon 1200 on my KT7A since early June, 2001 with almost no stability problems under Windows 98 SE. The only lockups that occur usually happen during some sort of disk access, even though they are fairly uncommon.
However...
Over the summer, a friend and I made five machines together using this mobo (along with its RAID brother). Three of the motherboards went to him for installation in customer machines, one for his personal use, and one went to me for the system I made for my personal use. ALL FOUR boards that went to him had to be RMA'd--talk about bad luck! Two were DOA, one died a few days later, and the last one (his RAID board, I think) made it about three weeks. ABit's support was worthless. He was pissed, so were his customers .
I think if you've made it two months, you're probably in good shape. Don't know about that northbridge fan, though. With my above experience with ABit, it wouldn't surprise me if they had some crappy northbrige fans on KT7As around the world. I'm sure there's some retailer that can sell you a replacement northbridge fan.
There's a slim chance I'll buy from ABit again, even though I hear many of their new boards are quite good (TH7II, KG7, KR7). When DDR RAM prices fall again, I'll probably replace my KT7A with either a ECS/SiS solution, or the board I routinely use in customer systems: EPoX's jewel, the EP-8K7A.
Good luck.