Fallout: New Vegas lead designer J.E. Sawyer has been interviewed on Xbox Live. Unfortunately, I don't have a Live subscription, but here's a summary:

• New areas will open up for the player depending on your reputation
• Not all weapons have mods
• "You only buy mods from stores" - once bought you highlight the weapon you want to add it to in your inventory and apply it
• They will cost you a lot of money
• Hardcore is seperate to difficulty
• Hardcore is more of a mechanical shift as opposed to just bumping up hp - he compares it to Ninja Gaiden
• There is a dehydration meter
• Dehydration meter will have impact o the player (most likely drop in stats)
• Being out in the desert in the day, as opposed to night, will have a greater effect on your need for food and water

If any of you have a Live subscription and there's any more interesting stuff in the interview, let us know!