Generally, presidents enjoy a post-election approval rating bounce. Nate Silver notes that since Harry Truman left office in 1952, the median bounce in approval has been 6.25%; the average has been 7%. The bounce for Obama is the smallest since Truman (who actually lost a percentage point); he has enjoyed a bounce of only 2%.
As Silver points out, this may represent the hardened partisan divisions of the present day. But it also makes it hard to argue that President Obama is sweeping into a new term on a resurgence of public approval -- and his inability to make that claim only weakens his hand in the fiscal cliff negotiations.