Erick Erickson, editor of Red State, told fellow conservatives to be realistic about whether recently released polls are skewed because Democrats are over-sampled in them:

I do not believe the polls are all wrong. I do not believe there is some intentional, orchestrated campaign to suppress the GOP vote by showing Mitt Romney losing. I actually believe that Mitt Romney trails Barack Obama. I think Republicans putting their hopes in the polls all being wrong is foolish. But I also believe the polls are reflecting a bigger Democratic strength than is really there.

Erickson added that "I’ll concede that Barack Obama is ahead, but I will not concede he is ahead by as much as some polls are showing." 

Here's an explainer by the Fix on how pollsters determine samples, and why the party ID argument is incorrect.