Contrary to the popular opinion, I actually like the way Karma effected your ending slides ever so slightly in NV, though I dislike the fact that Neutral was just the Good slide with dialogue cut out.
I like it, too, but the karma system itself is messed up. I always have very good karma in New Vegas just because I kill fiends, ghouls and powder gangers who attack me. There is a lot of nonsense stuff - killing powder gangers gives you good karma, but healing injured powder ganger gives you good karma... but killing him gives you good karma. And of course stealing from powder gangers (or other evil characters) gives you bad karma. Even if they're dead because you killed them before (which gave you good karma).
Also, karma system is negation of Fallout concept - there's no black and white, every choice has two sides and sometimes you don't know what's good and what's bad... but, of course, there's a karma meter which tells you, so don't worry.
And I don't agree with some karma penalties, for example eating dead people with cannibal perk - I don't see why is it bad (unless it was some innocent person whom you killed just to eat them), living in the wasteland is supposed to be harsh and it's not like a dead person is going to need their body.
In Fallout 3 karma system is broken beyond believe. It's nonsense how your karma reflects your reputation, for example - when you get bad karma by stealing stuff (and no one has seen you doing it), people know you're bad and don't like you (except for those bad guys who gives you random useless stuff just for being evil). There are also people who don't like you because you're good and hire mercenaries to gun you down. What.
Killing people in virtual reality (which was the shittiest part of this already shitty game) gives you bad karma, but killing them in different way gives you good karma.
This good&evil system which was presented as the great feature in Fallout 3 is just treating player like an 8 years old kid. In New Vegas it is fixed a little and plays a minor role, but it's still bad and unnecessary. I opt for removing it and expanding reputation system instead.