seems like the known Airport/KP issues after the new updates. as others have said, your only choice would be to re-roll the Atheros drivers to the previous version or buy a Airport Extreme (which works flawlessly).
I had a netgear wireless router that worked ok with my powerbook 12", but when I got my MPB SR and was setting up a new MB for my mom, those 2 new machines (both with N wireless cards) were not happy. I bought an AP Extreme which I was planning on doing anyway and everything is great. FYI: I haven't installed any of the AP updates after seeing so many complaints here.
One thing to look into regarding loss of signal is microwave use. I haven't tested my new APX setup, but the connection with my netgear would grind to a halt when I turned on the microwave. If you are in an apartment building perhaps that is an issue to look into.