Fallout: New Vegas lead Josh Sawyer has been interviewed presumably by the OXM crew, and the interview is up on XBox Live. Not having an XBox or a subscription will kind of hamper your efforts to check the interview out. Luckily, there's a basic summary of things here:

1. New areas will open up for the player depending on your reputation
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

Spotted @ No Mutants Allowed