I just wanted to ask you guys if the size of my save file is normal for the playtime I've had so far, which is 45 hours. After maybe 3 or 4 hours of playtime I get lag, mostly in crowded wide open areas, like Whiterun for example. If I turn off the console and restart, the game behaves normal again for a few hours.
So far I've done about 3 main quests, clearing up a few dungeons, college of Winterhold and a couple of sidequests + joining the Dark Brotherhood.

I'd say it's normal, but it all depends on what you've accomplished in the game. My current character has about 110 hours and the save file is somewhere between 11 and 12MB large. I've done 3 or 4 main quests, the DB questline, the Thieves Guild questline and the Companions questline + a crapload of misc. objectives and 4 or 5 daedric quests.

I'm currently in the process to try to decrease my list of active quests to see if that helps with the save file size (some people have implied that it does). So far I think I've managed to decrease the list by approximately 50%, but I've yet to see any significant change in save file size - it still fluctuates between 11 and 12MB.

File size isn't based on playtime it's based on how much you've interacted with the world... At that ammount of time I had over 10Mb save file on my first character and I'm pushing that much time on my new character and only have about 4 Mb... It all depends on what you've actually done... One thing I've found that raises it is if you are carrying alot of stuff in your inventory instead of putting it on a home or something... Also saving outside takes more memory than saving inside of a building...

I can save you some effort right now... It won't... The save file doesn't reduce in size from completing quests as it has to remember all the changes from having FINISHED those quests as it would have to remember what's going on DURING them...

Perhaps a rather noobish question, but how do you determine your overall save file size (PS3)? Would it be by looking at the last save description?

Well, I'm going to do the quests anyway so it's not so much an "effort". At least not compared to the ludicrous "Wait for 30 days ingame"-theory

Correct!

i personally think your save is quite small im 40 hours in on my un patched save and thats fluctuating between 9.2 and 9.4 MB

i'm about 120 hours in and my save file is 13MB. Solitude and Whiterun are a nice little slideshow for me. If i play longer than 2 or 3 hours at a time, the whole world is a laggy mess. I also have broken quests.

It's right under the save file information. At the bottom you'll see a number like 5437KB, which in this case translates to a 5.4mb save file.

Just wanted to update my situation: I'm now at 80 hours of gameplay, my savefile is 8.5 mb. I finished the Dark Brotherhood missions, Greybeards and a lot of misc quests including about 6 or 7 Daedra items. I've had no freezes during my playtime until now and no glitches. The only thing that is obsessing me is the lag. To avoid most of it, I restart my console every hour or so, mostly after I finish a quest. Also, I never keep more than 2 savefiles at the time. I didn't buy a house yet, I keep all my stuf in Anise's cabin. I'm not sure if I'm gonna buy one, freaks me out to think that it could cause more lag. What do you suggest guys?

17 MB on first character, dont play that one anymore lag / freeze and bugs, my new one is 24 hours playtime and 7 MB getting a little jittery , started at about 6.5 MB

I don't think that it is buying an house that starts the lagging. Then you restart the PS3 every hour anyway, so you won't have many lag issues.

I'm prone to believe that the best approach to reduce the number of glitches/lags is to stick with a quest until that is completed. Doing so the game should follow its normal workflow. Having no conflicts with other quests all of them should close fine. Well, unless one sides with the wrong faction which if I understood correctly should break the main quest. But that would be a design error, not a bug. In any case I left the main quest last and now I think it was better to finish it first to get the best shouts. It's kind of dumb, actually.

my first character got about 185 hours 16mb save and its not playable anymore. Made a new one that currently has about 25 hours 6.5mb save and the lag is starting.

The patches tend to keep the file size from growing as quickly, a stopgap measure only and the lack of info coming out on 1.4 suggests to me that they are struggling, pity.

Closing in at 100 hours of playtime, filesize is now almost 10 mb, 9,789 to be exact. The game is fast becoming unplayable. I'm doing the Companions quest line so I have business in Whiterun quite a lot. The low frames/lag/framedrops appear within a few minutes of playtime now. The game is a [censored] slideshow. Still no freezes and only one unfinished quest(Troubles in Skyrim).
What in the name of God are you doing Bethesda? What in the name of Jesus are you doing, Sony? How is this possible in 2012??? How can we be treated like this? I'm the biggest idiot in the world, this has happened to me recently when I bought Rage for the PS3. I am still giving them my money and they still [censored] on me.