After all, it's going to be hard to straddle the line between the NCR and the Legion, two of the game's most important factions, so you may want to try to do quests for both of them that don't necessarily affect one another. In a very overarching sense, you simply won't be able to please everybody, which is why it's probably a good idea to try to spread out questing (and side-questing in general), to please as many factions as you can before people start inevitably getting pissed off at you. Now believe it or not, karma and your standing with various factions plays directly into questing. Karma still exists in Fallout: New Vegas, but it's a much more nebulous term, because what's really important in New Vegas isn't what your overall karmic standing is, but rather what your standing is with the game's many factions.
But things are even more complicated in New Vegas, since all of your decisions aren't based solely on good or bad karma, which was the behavior governor of Fallout 3. One of those cues is in terms of undertaking quests and making choices therein.
While Fallout: New Vegas is an all-new game, it takes a cue in more ways than one from the game that precedes it, Fallout 3.
