I apologize in advance if this is post is of interest only to survey research nerds. But I find the following chart from FiveThirtyEight fascinating:
It seems to suggest cell phone-only users (presumably young people) are enough to swing most polls about 2 points toward Barack Obama. No telling how this translates into voter turnout and actually results.
One more thought: while many may think of cell phone-only users as just young people, it is increasingly common way for working class and poor people have phones. So, it may include many black and lower income voters, too.