The Democrats get surprized every year, because most polls overstate their support by 3-5 points. Rasmussen and Zogby tend to be closest; ignore the others. The Republicans are going to hold the House and Senate, despite the fact that Nancy Pelosi is already eyeing the drapes and carpets at the Speaker's office.
To greatly oversimplify what happens, the MSM overlooks the basic numbers. About 30% of Americans consider themselves conservatives of one stripe or another, 20% liberals. The remain 50% also split 30-20 in favor of conservatives, though single issues, personalities, and the weirdness of general events can affect them more powerfully. The play of the MSM on those personalities, single issues, and weirdnesses moves a lot of easily-misled people leftward, creating the appearance of an evenly divided country. That's Newsweek's estimate, not mine, BTW. They estimated in 2004 that the dominant media was worth 10-15 points overall.
Democrats gain only when the numbers are artificially suppressed, by biased reporting, bad polling, or dumb luck. Without the constant reporting of how badly Iraq is going, and the constant ignoring of how well the economy is doing, the electoral slides back toward its natural divide of 60-40. The Foley scandal artificially suppressed the Republican gains which started in September. Unless the Democrats have another October surprize, the points will creep back.
How the change in media fits into this I don't know. There is rampant speculation on the blogosphere that this is all poised to change soon, but the results aren't in. And when I traveled last week, or when I sat in the hospital waiting room today, the news available is all MSM. Nightly network news and major daily papers remain the default position for credibility, no matter how many times they get shown up.