I talked to the TIPP pollster last week. While the don’t publicize their party weighting, he told me that they are only anticipating a 2-3 point gap favoring dems. This is not a poll that is oversampling dems by >5 points.
I think that's still over weighing the Dems. It should be even. If they are using the 2006 mid-term election they are in error. The Republicans did not turnout for the 2006 mid-term elections for various reason that were document here on FR, but they certainly are going to the polls in this election.
Here's another factoid to chew-on, in all mid-term elections, the electorate turnout (37% average) is about 20% less than presidential elections. You cannot use mid-term election models as a substitute for presidential elections.
However, we will see who is correct, and by all indications that we are seeing, it's not going to be the media and their pollsters.