So what can i do to decrease the quality of the mist (or particles, whatever)? because i find myself lagging quite badly in places with mist; places such as falmer dungeons and such.

Your quite on cue mate! I was about to post about the same thing.

Do you have an ATI card? My ATI HD5650M can run Markarth 30+ FPS no problem but has terrible, terrible unplayble lag and stuttering in Morthal.
Specular effects also seem to hammer my card. At the atronach forge under the College of Winterhold my game basically hangs up.
What's odd is that the game is still running at 30FPS, just lagging terribly.

I'm going to try and roll-back drivers to see if it helps.

Yeah, WTF did they do with the mist? Crysis has volumetric smoke that doesn't kill the performance like Skyrim does. The game is just badly optimised in a lot of areas, though it could be driver performance bugs as well.

Haha, I get the same.

It's not so much FPS problem. I play capped at 35fps and I still get 30-35fps in areas like the marshes around Solitude. But I get terrible, terrible mouse lag. Like literally I'll turn to the right and the camera will follow me about a second and a half later. I've found disabling some mist with the console can help, there's a lot of overlapping mist there and I think that's what causes it. Needless to say, come January and that will be one of my first mods to fix.

eh, how do you disable the mist with console commands?

And does anyone know any .ini changes to reduce the mist quality? Like to reduce the number of particles or something.

Fog in the distance is an effect due to the weather, you can't touch that.

However the mist in areas like the marshes are editor placed, as in they've been put there as an object by the developers. It's easy to open the console, click on a patch of mist and hit disable.

Smoke and mist effects kill fps in any game. Its not just skyrim.

"iMaxDesired=750 - This variable in SkyrimPrefs.ini controls the maximum particle count for particle effects like smog, fog and especially fire and spells."

Thing I've noticed though is that it's not FPS, it's mouse lag. Horrendous mouse lag, which suggests it's the engine having a fit.

And the problem with that variable is that you're changing things like fire spells. Set too low and fire spells look like you're throwing a red ball at the enemies.

I don't get any lag in misty areas, and don't have the best hardware out there either.

I do get stuttering in first person view sometimes. Could it be something to do with hyper threading?

That kind of mouse lag usually happens when the GPU is overworked and is being given commands faster than it can handle. After a second or two it's got many frames worth of render calls queued and the results of any input won't show for the length of the queue. I don't personally get that much input lag when looking into mist effects, but it's noticeable and my video card certainly gets very loud in any indoor area with mist.

You could even see this in Morrowind if you looked into the Propylon chamber particle effects from certain angles (Morrowind even has input lag with a GTX 560 Ti if you do that!). Just too many things being drawn on top of each other, there's no way a GPU can have the http://en.wikipedia.org/wiki/Fillrate to handle that unless its hardware is otherwise insane overkill for the resolution being used.

Limiting the video driver's command queue length to 1-2 frames may reduce the lag. The option's called "flip queue" on ATI and may need some external tool to mess around with. Nvidia calls it "maximum pre-rendered frames" and it can be found in the driver's control panel.

Try: http://www.skyrimnexus.com/downloads/file.php?id=736