Here's one reason political polling seems so screwy this year: More and more of us rely exclusively on cellular service. And finding cell users is pricey and hard. The folks at the Pew Research Center, who do lots of polling, estimate that it costs four or five times as much to find and interview cell users, screen out the ones who also have a land line, and interview a sample of those remaining. It wasn't a big deal five years ago, when only 3 percent of households were cell-only. But by the end of 2006, that had zoomed to 13 percent and could reach 25 percent this year. Why not just ignore cell users? Pew says they count now more than ever since they are a big electoral group: younger, more likely to be black or Hispanic, and less likely to be married or own a home.