Ha beat me to it....
OP sounds like a case of bloated save file, clearing the system cache and game cache along with a little " spring cleaning " may be in order.
5-8mb?!?! Well then it shouldn't be save file bloat, I'm a little stumped
edit.....
Still try clearing the system cache and game cache, this should help.
Skyrim occasionally lags for me but now that I have about 33 GB on my Xbox hard drive, I get less lag and my game doesn't freeze as much. Also, I realized that if you have Hearthfire, Dragonborn, and Dawnguard downloaded, you'll get way more lag than having no DLC's at all. Loading screens would be shorter as well.
Believe me, playing online or not won't fix anything. Tried it, nothing at all. You could try installing the game. I haven't played PS3 so I'm not sure if you can install games like on Xbox. That should help it a bit or you could delete others things to add more space on your hard drive but I'm not positively sure if that'll work. I don't know much about the PS3 since I don't have one but I might get soon, so if you can, try installing the game if it's possible, like I said.
Actually, it's been said that installing the game to your HDD is a bad idea, the game runs better straight off the disk.
Once again you have beaten me to the punch
Oh lol xD
I got my copy of Skyrim by redeeming a code so I had no idea of that. However though, it seems like the main problem for lag on Skyrim are the DLC's, at least for me. But I don't mind the small amount of lag as long as I enjoy the game and killing people sneaky-sneaky with my Enhanced Dwarven Crossbow.
I blame Hearthfire for my lag, once I uninstalled it all my lag and freezing went away ( for the most part )
I have only experienced really bad lag for the first time ever in the game, sometime after installing the DLC I got when it came out (although I can't be sure that was the cause) after playing the game for about 6-7 hours straight, something I rarely, if ever do. All I had to do in that instance was save my game, shut it down and then restart and voila, the lag was gone!
he may even need to restart his pc if he has been running it for quite a while.