It's ALL about Turnout
This year's results, like those in all non-Presidential election years, will all come down to turnout. Who votes determines who wins. Look at these numbers from early voting in Broward County--a county, by the way, with a huge edge in Democratic registrations (from the Sun-Sentinel):
Countywide, 12.5 percent of all voters have voted with 8.4 percent by early voting, 4.1 percent by absentee. That includes 12.7 percent of the total registered Democrats in the county; 13.4 percent of the registered Republicans in Broward; and 7.7 percent of the third-party voters that had cast ballots by Monday.
I call your attention to two things. 1) Tell me again how enthused the Democrats are and how discouraged the Republicans are. It's conventional wisdom, but it's dead wrong. These predictions of massive Democratic gains are based on that model...which so far does not match available evidence. (But why let facts get in the way of a good political storyline?) In Broward county, Republican early/absentee voting is running almost 10% ahead of Dems! (That's not votes--that turnout percentage, but if a trend like that holds...) Yes, it's always dangerous to extrapolate from small sample sizes, but real world facts and pundit opinion are not lining up.
2) Those polls that are showing a large segment of "independent" voters are worthless. They may or may not be accurately reflecting what the voters think, but as a tool for judging the election results, they have ZERO value. These people, especially in an off year, just don't vote in large enough numbers to matter.
I'm saying it again. There are (I think) going to be some hugely surprised people by this time tomorrow night.