You'll forgive me if I doubt something from the mouth of Al Franken regarding the "truth" as far as bias. I'm sure Rush Limbaugh's book shows them worshipping at the liberal altar. If you'd actually like to display the FACTS of your study, feel free to post that though, so we can actually see who did the study and the questions that were asked.
I've found this compilation of polls to be very informative on that aspect.
Media Bias
One thing is for certain. That a disproportionate majority of media personnel are self described liberal persons. Now whether that leaks into their reporting, writing, etc.. is a matter for debate. However, I find it highly unlikely that one can totally disassociate from your beliefs when writing a story.
What has recently furthered my belief that they lack the ability to do so, have been the recent scandals involving Ms. Mapes, a vehemently self described liberal, basically threw all sense of journalistic integrity into the fire to get her viewpoint broadcast on the air. That CBS would even employ someone who so obviously portrays a bias makes me question what other media out there similarly overlook such indiscretions. The Halperin memo draws into question what exactly is ABC's agenda.
When you really boil it down though, it's the viewers that decide what networks are too liberal or too conservative for their outlook. I consider myself a centrist overall, liberal on social issues, conservative on economic issues. I "test" that area as well on the political question sites you can access on the web.
Excluding the pundits which inhabit every network, my overall opinion is that:
CNN: Slightly left social, Slightly Right economic
FOX: Moderately right social, Slightly Right Economic
MSNBC: Don't watch enough to have a clue.
CNBC: Never heard of it.
ABC: Slight left social, centrist economic
CBS: Moderately left social, slightly left economic
NBC: Slightly left social, Centrist economic
PBS: Slightly left social, slightly left economic
Generally speaking I watch either NBC or CNN so I have a better idea of what they do overall. I have seen relatively unbiased reporting on all of the channels to some extent, but every so often, particularly when there is a "good story" the reporter or program managers bias becomes so obvious as to be laughable. I can't honestly say I've ever seen an unbiased news source because I just don't think it's possible. The only way that would be possible I think is for reporters to report the facts of the case, rather than making it into a story and eventually decide which "facts" are important enough to include and which ones can be left out in the interest of their 45 second segment.