I notice all kinds of variation. I listen to the iPod a lot, but when not listening to the iPod, my radio listening is (in descending order of priority, just going by amount of hours listened) is generally: 97.7 (KFFG - KFOG's Los Altos transmitter) -> 104.5 (KFOG - this gets sketchy south of 84 or so on 101, where the Los Altos broadcast works better), 107.7 (KSAN - 'The Bone' and certainly not the country station anymore), 98.5 (KUFX, 'K-FOX', but there's no real furry connection, just Sharks games and classic rock) and 105.3 (KITS, I think, alternative/whatever).

I'll notice that depending on weather, which KFOG/KFFG station gets better reception in a different area can dramatically change.

Of course, I haven't been tracking seasonal drift, and my car is digitally tuned.

Either way I have long known that 280/Page Mill is in a little bowl that's a black hole for radio reception of all sorts.