So my Fallout experience has been largely pleasant so far, with two exceptions: the lost saves thing (hooray for a fast response! thanks Obsidian!) and an occasional crash. Now, when I say crash, I don't mean a normal CTD, I mean a complete lockup of the entire computer: completely ignores keyboard input, has to be hard shut down with the power button. And I found that when it had a crash like that, it tended to keep crashing for a while; even worse, Windows started getting unhappy about restarting from these crashes. First it would just take a bit longer than normal to finish starting stuff in the background after I logged in. Then a lot longer. Then 30+ minutes for it to even show my background after logging in. Then failing to even launch Windows properly, and constantly cycling back to a "Do you want to start in Safe Mode?" prompt. I found that just leaving it alone for a couple hours tended to resolve the issue for the most part, so hey, that's obnoxious but not the end of the world.

Then it happened to my roommate when he was trying to play FNV, and when his froze, down in the bottom right was a nice, "(my Steam Name) has started playing FNV" notification. I thought about it and realized he'd always been playing when I had problems. A quick test was conducted and we quickly confirmed that whenever one of us launched FNV while the other was already playing, the one already playing crashes. The burden of this falls largely on me, as my roommate's computer doesn't seem to mind coming back from these crashes (he's got a Mac with Boot Camp, dunno if that's relevant), and he tends to play in short spurts anyway (play for 45 mins, do something else for 45 mins, repeat).

Posting this from my laptop, will try to put up a dxdiag tomorrow when desktop is willing to boot up again. Roommate has turned off all Steam notifications, we'll test if this resolved issue later (again, once my desktop will launch Windows properly). Has anyone else had an issue like this, specifically with multiple people playing at the same IP address? Could this be a leftover bit of Fallout 3 code? Windows Live (poorly designed PoS that it is) won't accept more than one connection per IP, so when we both played Fallout 3 at the same time, one of us would get kicked off Live; not a big deal since a Live connection wasn't required to play, it just meant your achievements didn't get counted until you reconnected to Live (kicking the other person off). But that initial connection to Live was the game's DRM; is some variant of that code being used in FNV?

You could give the Steam offline mode a try. The game doesn't require a live internet connection all the time. However, I did have a crash today that I think may have been due to my internet connection dropping. So Steam stuff happening in the background can have an impact and turning to offline mode should avoid a lot of that.