Well, pretty divided, judging by evidence presented by political scientist Matthew Levendusky in his recent book "The Partisan Sort: How Liberals Became Democrats and Conservatives Became Republicans" (University of Chicago, 2009).
But it's important to distinguish masses from elites here. Elites -- those with high political knowledge and high participation rates -- have in recent decades adopted more extreme attitudes rightward or leftward. Levendusky defines this process as polarization. For evidence of how fashionable extreme views of politics have become among elites, watch MSNBC or FOX news any night.
The public, on the other hand, has not tended in more extreme directions but has undergone sorting by which the GOP has become more uniformly conservative and Democrats more uniformly liberal. That has made the public a bit more polarized -- oriented toward political extremes -- but not as much as the elites.
There is good and bad in this mass sorting. On the positive side, "sorting ties voters to their party, which in turn allows them to make better decisions. Strong party ties are vital to healthy democracy: party is the vehicle through which ordinary voters can connect their underlying values to a vote choice" (p. 138).
But sorting also "invites into politics passions that cannot be easily brokered or negotiated" (p. 138). So "if citizens can participate meaningfully only by relying on political parties, then we should decide whether the benefits of such participation are worth the costs" (p. 140).
Among the public, those benefits are worth the costs. The 19th century featured strong partisanship and very large levels of electoral turnout. That can happen in America again.
It's the elites who need to clean up their act. Rhetorical food fights, name calling and boorish behavior in institutions of government or the national media set bad examples for citizens and probably dampen civic enthusiasm. It's possible to be polarized and polite. The public deserves better from their elites. Will they get it?