I canvassed for Kerry in 2004. We were instructed to hit a neighborhood that had clearly been hit far too many times already as a number of people would answer the door with "you people again?" followed by admonishment that they were now thinking of voting Republican just to spite us.
I think it's a lot easier to preach to the choir, so much so that we do it well past the point where they resent the sermon. My legislative district has a Facebook page... Run by the daughter of my state representative. And it's been so full of bile and hate that I'm really hoping she loses so I can say I voted for her opponent despite the cash from Monsanto... Simply because her posse be bitchez.