MTV Multiplayer is the latest website to dish up a press event-based preview of Fallout: New Vegas, though their focus is almost entirely on the game's combat system enhancements (versus Fallout 3).
The most prominent fix during our hands-off demo was the ability to bring up a weapon's iron sights. In practice, it both steadied the weapon and increased accuracy. But more importantly, it allowed for the action to continue without engaging the VATS targeting system (which was how I handled nearly 99% of combat in "Fallout 3").
Obsidian also chose to expand how players use particular weapons by including what appears to be a rather simple but dense weapon modification system. Specific upgrades like extended magazines, mountable scopes, and recoil dampeners all change a given weapon's effectiveness in combat, but they are also visibly rendered on your weapon. So attaching a fancy new upgrade won't just be part of a numbers game, you'll see it right there on the weapon. Upgrades are weapon-specific though, so don't expect to be able to carry over your mods from gun to gun.