According to PEW the fastest growing group of voters in the US were liberals, who are socially and economically left wing. They went from about 10% to 19% of the electorate between 1999 and 2005.
I have no idea if the liberal base is still growing. However all the disaffection about failures of the democratic congress and white house to get reform is probably going to push the democratic party further to the left because unions and progressives will put efforts into primaries and holding centrists accountable.
At the same time the GOP lost power because they were too far right. But the response from the right has been to go further to the right. I think even Gingrich is frightened by what an unqualified extremist Palin is. The right wing media and evangelical base wants to go further right. So support of people like Palin, Toomey and Hoffman is going up. People on the right are openly talking about violent coups while people on the left are trying to create a party more along Kucinich’s mold.
So what is the long term result? What happens in countries where there are 2 major parties that become extreme? Governments made up of communists/socialists vs militant right wing authoritarians usually don’t seem to end up well.