Democrats are saying that they have polling that shows them ahead or tied in 34 Congressional districts held by Republicans. They need to pickup 25. This is by no means a slam dunk, but there is real hope that the Tea Baggers can be shown the door.
The best polling is done by both parties, and contrary to what the right-wing cranks will tell you, they don't lie about results. Even the Republican party just keeps the results to themselves rather than lie about it, it's an issue of credibility with their own supporters. Not that the Republicans have much of that, but they leave the heavy duty lying to the billionaire funded professional liars.