I'm about 15 hrs in, save file 4mb, no lag at all (yet). I'm playing on a fat 80GB MGS4 bundle PS3, upgraded HDD to 540Gb.

Just wanted to throw out there that it looks to me (anecdotally) that most ppl are experiencing the lag first in Whiterun, then it "spreads" to other aspects of the game, or that the word Whiterun seems to be commonly associated with posts dealing with lag.

Is it possible there's some unholy alliance between save size and the code for Whiterun that's triggering the FPS/lag issue? Thoughts, anyone? Am I accurate here?

i think its more to do with how much stuff you do in the game i.e go raiding loadsa dungeons and caves cuz it saves evrythin you do and loot and kill it just gets bigger and bigger and then it overloads