Is Barack Obama as polarizing a president as Bush? David Paul Kuhn at Real Clear Politics makes the case:

Obama ... only matched by George Bush, has the most polarized public approval rating since the advent of polling...Last year marked the most polarized period in Congress since 1953, when Congressional Quarterly first began quantifying partisanship. Lawmakers now vote along party lines 90 percent of the time.
Tempers may be cooler now than during the vicious election of 1800, when foes called John Adams a hermaphrodite, but partisan anger is running hot enough for pundits to to ask questions. Why does polarization pay? And what do we lose having a country of partisans? Here are some thoughtful answers from the blogosphere and the op-ed pages:
  • Both Parties Forget Their Extremist Fringe  In a post on Secular Right, Heather Mac Donald argued that both parties are guilty of exaggeration and double-standards. "Democrats," she explained, "in portraying right-wing hyperventilation over Obama as a manifestation of covert hostility to blacks, forget the insane Clinton conspiracy theories that grew like kudzu even in the highest reaches of Republican opinionizing. ... Republican pundits, in portraying Obama as an unprecedented danger ... forget their own dire warnings about the Clintons as the end of civilization." Furthermore, Republicans previously outraged by attacks on a wartime president seem to have forgotten that the country is still at war, while Democrats who cheerfully "participated in Bush-bashing" are now appalled by "Obama-hatred." Why, she asked, do pundits feel the need to contaminate "unimpeachably accurate ... analyses" with "loony-bin allegations"?
  • It Pays To Be Partisan, was David Paul Kuhn's simple answer on Real Clear Politics. "From the partisan media to the modern campaign, an entire industry flourishes on polarization. Partisanship earns and spends billions annually" for both parties. The "gerrymandering of congressional districts" forces representatives "increasingly [to] depend on partisan voters," who, whether Democrat or Republican, increasingly "segregat[e] by choice" in socializing. The results, he argued, are clear:
Republican Rep. Joe Wilson yells "liar" during President Obama's health care address. Wilson apologizes that night. GOP greybeards scold him. But one week after, Wilson and his opponent raise more than $3 million combined. Partisanship literally paid off.
  • Paranoia at the Root of Extremism   One result of the summer's polar politics has been conspiracy thinking, said Arthur Goldwag in the Chicago Tribune. He discussed conspiracy theorists as the pinnacle of extremist thought. "America's ideologies and actions are all too often driven by cynical political calculations, weak moral characters, authoritarian impulses. But conspiracy theorists don't register such shades of gray." Instead, they "believe they have been vouchsafed a revelation about the true nature of the world. As they see it, there are no tragedies, no accidents and mistakes, no good intentions gone awry."
So what are the casualties of this polarization of American politics? Kuhn describes it as a sort of internal xenophobia:
It's the partitioning of not merely thought but American experiences. Each tribe has come to view the other as nearly foreign. And what is foreign is therefore dismissed. The cost is compromise. And the outcome is a paralysis of governance.