hmmm... It seems that too many people forget one thing...

What is your monitor refresh rate?
If you have a flat panel you probably have a ~70Hz refresh rate. That means your monitor is showing 70 images per second.
What happens if your graphic card generate *put whatever high number you want in here* FPS? really nothing, your monitor is still showing 70 images per second.
So, for me, does not make sense that some people get smoother sensation when running at 250 FPS than running at 80 FPS cause they are seeing 70 images per second in both cases

If I'm wrong please let me now

To be on topic... You may activate VSync only if you're getting page tearing (or in older games), but you may activate FPS limit and set it to 100 (for example) to prevent graphic card work for nothing

Some of you guys can't be running very high resolutions, my 6600GT was pretty good for my old 22" at 1680x1050, stable 40-50fps with mid range fsaa and af. It just couldn't cut it with the new 24" at 1920x1200, the 7600GT I tried for a while was an improvement but it's only now with an 8800GT that I get a rock solid 50fps at all times with all in game settings, fsaa and af maxed.
If your going to mention what settings you use you should really also mention the resolution.

One thing I've noticed with LFS is that a stable fps is more important than a high one, a stable fps of 50 will be smoother than one that fluctuates between 70 & 80 fps say, well to my eyes at least. I always limit the fps in LFS to avoid this and wonder if this effect is why some people feel LFS isn't as smooth as some other games.

I'm actually also having some stutters with LFS sometimes, although the FPS doesnt really drop below 45 or so. And in the starts FPS of 30 is actually quite horrible and hard to control?

And there are some places on Aston, which always cause some sudden FPS drops, it doesnt drop under 40, but I can still feel it also besides seeing a unexpected drop from the numbers.

One of the place is before the final chicane on AS GP. Also one is somewhere around the hairpins in the beginning of 2nd sector.

1650 x 1050
7800 GTX
22" Samsung

AA and AF were max for a while, but I took them a step down, cause it seems smoother, although the FPS didnt drop below 30 before either :|

What's your CPU? What's your HDD? Any background stuff working?

Dual Core 3800 + AMD

Dunno bout HDD.

I always close most of the stuff from task manager right after I restart my PC.