Bethesda's Senior Producer Jason Bergman took some time to answer some fan questions on Sony's Playstation Blog. Some of them are downright inane, but there are still interesting bits like this:

Will there be any Vaults to explore in New Vegas?

Yes there are! We have five different Vaults in the game. They serve as unique dungeons, and depending on what path you follow through the main storyline, you may have to venture into one of them to retrieve something.

http://www.gamesas.com/index.php?/topic/1120863-community-questions-answered-spoilers-obviously/