Although I am one of few liberal-minded people who admit that many mainstream outlets may have slight accidental liberal slants (CNN being most well-recognized, along with NBC and ABC; I still don't think CBS is liberal), I don't think it will affect anything.
First off, any biases (except probably Fox's) are so subtle it's only barely recognizable even to the well-trained viewer. If you're watching just the main news segment (not O'Reilly, Cavuto's World, or someone else offering his opinion), you can barely tell differences between stations. One day watch CNN for a while and switch over to Fox. The news stories are almost identical.
Secondly, as a recent CNN survey actually proves, viewers stick to their camps. They watch the stations that most reflect their viewpoints. Liberals tend to watch CNN, and conservatives overwhelmingly watch Fox.
