“Fallout: New Vegas uses Steamworks for achievements and other features (such as friends lists, cloud storage of user preferences and so on). Use of Steam will be mandatory at retail. So what does that mean? We’ve implemented Steamworks in as light and unobtrusive a way as possible. Yes, you will have to install Steam when you install Fallout: New Vegas if you don’t already have it. And yes, you will have to be online at the time of that initial install. However you can install the game on as many systems as you want (with no restrictions!), and you do not have to be online to play the game after your initial activation. Not only that, but once the game has activated on Steam, you can throw out the game DVD entirely and just download the game over Steam. If you don’t even have a DVD drive, you can just take the CD-Key from the box, enter it into Steam, and download it without ever using the disc at all.
For those concerned, this will have no affect on mod development whatsoever. Modders will still be able to create and distribute their plugins the same way they have in the past.We made the decision to use Steam after looking at all the various options out there and decided that it provided the best, least intrusive experience for PC gamers. We think you’ll agree.”