David Corn says the Edwards endorsement doesn't matter much:
Having John Edwards at his side during the general election will help Obama to a limited degree. But that won't do much to populist-ize the likely Democratic nominee. Obama--as would practically any Democrat--will come across as a populist and working-class advocate not by campaigning with Edwards but by campaigning against McCain.
But it would be a mistake for Obama to adopt any of the anger of Edwards' 2008 run. 2004? Sure. But there's a difference, and an Obama lunge for the Shrum line would be disastrous.