Mine is doing the exact same thing. My MBP is getting intermittent wireless signal strength as is my wife's MB. I added a Airport Base Station in the room we use the most and it hasn't helped. It seems to be worst when it's actually performing a backup but I just turned Time Machine off and I still have only 2 bars - 8 feet from the Base Station and 25 feet from the TC. Seems pretty ridiculous to me.
Also, when I try to access my TC it takes forever for the screens to load - minutes, not seconds.
I don't know if it was a software upgrade or if my machine is tanking, but the fact that my wife's machine does it too makes me think it's the TC.
On a side note my MBP battery only seems to last about an hour or so now. After spending two grand on a laptop these two issues are driving me crazy.
Any ideas on the on what to do with the TC? I plan to call AppleCare tomorrow but I don't have high hopes.