Despite this being a known issue since Fallout 3 was released, despite it being fixed for Fallout 3 by a user-made patch using FOSE and custom-made .dll and .ini, here it is again, a couple years later. Lordy.

Hopefully, the guys who made FOSE and the Stutter-Remover will have a headstart and fix this game-ruining issue, http://www.gamesas.com/index.php?/topic/1069833-relz-fallout-stutter-remover

You'd think this, and the simple 'wacky mouse acceleration' problems, which have been solved by the community, would've been fixed from the start with New Vegas by the development team.

It's most likely an engine issue which the developers can't be arsed to fix because it works ok for the xbox 360