That's interesting, but thankfully they only had 395 tweets so I wonder if you can get something really meaningful with a set of data so small. Looks like there's some correlation with Rommey's voting states though.
Of course it's correlated with the red states; when the person they didn't want to see win won, they said anything they could to degrade him. Certainly the n word is the easiest and most offensive word to throw out, but that doesn't necessarily imply racism. Though I'm not defending their use of that extremely offensive word, it's highly disingenuous to equate it to racism.
A frustrated exclamation of a horribly degrading word to express their anger != A view that African Americans are inferior.
It certainly doesn't show class and I'd bet you'd surely find a higher proportion of racists among those who tweeted that word, but calling them all racists? Wrong.