Fallout 3 microstutter fix
Fallout 3, Fallout: New Vegas, and Elder Scrolls IV: Oblivion all use the Gamebryo video game engine. Gamebryo has some weird quirks on the PC and the one of the most obnoxious is microstuttering. Microstuttering manifests itself with tiny persistent jerks and delays while moving, even if your FPS is high and stable. The root cause seems to be the way FPS and game time are linked. One solution is to unlink the the game's timing from FPS by editing values in the cfg file. This solution does fix the stuttering for most people, however the downside is that time slows down if FPS drop. One method to deal with this is cap the FPS using some sort of software and set the maximum FPS low enough that your machine won't dip below. However using a low enough FPS can lessen the experience somewhat.
Another solution is the Fallout Stutter Remover. Originally it was developed to fix the microstutter issue in Oblivion, it also works in Fallout 3 and Fallout: New Vegas because they all use the same underlying game engine and are prone to the same quirks. You will also need to install FOSE, it's an addon to Fallout 3/New Vegas that extends the scripting language used by some Fallout mods.
I personally use the Fallout Stutter Remover, it seems to work OK and doesn't seem to have any side effects that I have noticed. I find it interesting though that Bethseda never fixed this issue themselves.