Whatever political polls really mean, they do affect public perception and public perception affects campaign coverage. To that end, Nate Silver at FiveThirtyEight calls out RealClearPolitics for bias, alleging that the site cherry picks poll results that favor John McCain to include in its rolling averages.
Whether fudging the numbers would actually help McCain, or hurt him, is hard to say. On the one hand, favorable polling might bolster enthusiasm for the candidate, influencing volunteerism and donations. On the other hand, it might instill a false sense of security that slows a necessary change in tactics.
Either way, the real clear issue here is ethics among pollsters. I'll post any responses I find to Silver's allegations when I find them.