I'd say it depends on the system...
I really don't like (serious) infighting in DnD - IMO, the game is set up such a way as to require teamwork. If the players are at each others throats, I find they get little done and tend to be ineffective. I'm viewing this as really serious disputes, where the PCs either fight or screw each other over. On the other hand, bantering and friendly abuse just add to the game.
If I see it happening, I'll try to steer the players in another direction. Possibly have an outside event interupt them... or just an out of character 'play nice' kind of comment.
For some other systems, I'd say it's par for the course and it wouldn't be the same game if the PCs didn't plot against each other. Paranoia, Vampire and Ars Magica really spring to mind as examples of those type of games.
Our last Ars Magica game worked out very nicely. 6 PCs and a number of topics to disagree about... mostly Pagan religions, overthrowing kingdoms, consorting with a Demon, and the Crusades... A mixed bag with plenty of room for squabbling. Was fun, found certain people allied over certain issues, but were bitter enemies over others. The way their system is set up, mages are forbidden from killing each other - so it was basically a lot of plotting, backstabbing and theft going on. Kept trying to engineer the death of the demon consorting wizard, but he just wouldn't die.

Definitely felt like a tower full of selfish and powerful wizards!
Think
FreeTheSlaves, has hit the nail on the head about what separates a 'friendly' argument from something worse. Whether the players like each other out of character!