There is a new interview with lead designer J.E. Sawyer talking Fallout: New Vegas available, but only to Xbox Live users. A user on the BGSF runs down the points discussed.
1. New areas will open up for the player depending on your reputation Thanks No Mutants Allowed.
2. Not all weapons have mods
3. "You only buy mods from stores" - once bought you highlight the weapon you want to add it to in your inventory and apply it
4. They will cost you a lot of money
5. Hardcore is seperate to difficulty
6. Hardcore is more of a mechanical shift as opposed to just bumping up hp - he compares it to Ninja Gaiden
7. There is a dehydration meter
8. Dehydration meter will have impact o the player (most likely drop in stats)
9. Being out in the desert in the day, as opposed to night, will have a greater effect on your need for food and water