"The 'cellphone effect.' In 2003, just 3.2% of households were cell-only, while in the 2010 election one-quarter of American adults have ditched their landlines and rely exclusively on their mobile phones, and a lot of pollsters don't call mobile phones. Cellphone-only voters tend to be younger, more urban, and less white — all Democratic demographics — and a study by Pew Research suggests that the failure to include them might bias the polls by about 4 points against Democrats, even after demographic weighting is applied."This will make the "science" of polling even more suspect. It's a factor I hadn't really considered until now, but everyone that I know who has dropped their landline for a cell-only life is definitely in the Democratic profile.
On the other hand, those people most likely to skip voting entirely are also in the exact same demographic.