Remember when Bethesda asked Fallout fans to submit New Vegas questions via Facebook and Twitter? Even if you don't, you'll be happy to hear that the answers to those questions have started to arrive:
Will the PC retail game be able to be activated via Steam? Wow, Steam seems to be really gaining, uh, steam. Oh, and there's even some new concept art to feast upon.
Jason Bergman, Senior Producer at Bethesda Softworks: Yes. Fallout: New Vegas will fully utilize the Steamworks SDK. This means that retail PC copies will activate via Steam. We are also using Steam for achievements and other features (but not multiplayer, of course. FNV remains a single player only game).
You hinted at multiple ammo choices being available. How deep are you going with that? Will that only be regular and AP ammo?
JS: What ammunition sub-types are available to the player depends on the base type. Not all ammunition types have standard, hollow point, and armor piercing variants. For example, there is no armor piercing .22 ammunition. In addition to "standard" ammunition, hollow point and armor piercing are the two most common variants. 20 gauge and 12 gauge shotguns have slug variants in addition to the standard (buckshot). Some calibers also have +P (overpressure) rounds, military surplus rounds (bought in bulk, increased power, increased wear on the weapon), or hand loads. Hand loads are always built at reloading benches in the world and can take a number of different forms. For example, you can craft .308 Jacketed Soft Points or .45-70 Gov't Semi-Wadcutters with very "hot" loads.
Energy Weapons and Explosives can also use ammunition subtypes. Some energy ammunition has "over charge" or "bulk" variants, the former being high-powered but damaging to the weapon and the latter being cheap but under-powered. 25mm grenades (used in the grenade machinegun) have a high explosive variant and 40mm grenades have an incendiary variant.