I don't think it will be close enough to be contested (fingers crossed).

The losing side always claims fraud

Of course. One side has been claiming "fraud" for a year before today to gear up for today. You ain't seen nothin' yet.

They pulled a lot of crap in FL and OH. If it was close in those states, I would say yes.

I think that NJ and NY are probably tipped enough blue that they won't be contested. But the electoral votes for any combination of CO, WI, OH, even FL, VA will be contested and delay results if the vote difference isn <1M. I think early voting, provisional and absentee ballots are counted differently in every state.
How ugly? 2000 was ugly.

With the election being so close, I think there is a good chance the results could be contested. It is hard to Imagine how some of those effected by Hurricane Sandy will be able to vote. There could also be accusation of voter fraud. I think we have not yet seen how ugly this election can get.