Actually, I don't think the media is terribly liberal (although I am fairly conservative). I think what has made so many conservatives think the media is liberal is the way that they canonized Bill Clinton. I don't think anyone has ever gotten the slack from the media that Old Bill has. I think that the media folks, generally a liberal crowd, genuinely felt that Bill was going to be an important president who would make a big difference and they tried to help him make it happen. I don't really fault them for having a sincere belief.
Bill is still getting a free pass, but I think the media (as if it were a single thing) has a generally sour taste in their mouths from Clinton. He was their boy, they backed him to the hilt, went to the mat for him and all they got from it was embarassment.
The interesting thing to me is that Al Gore is not getting anything like the "get out of jail free" ticket that Bill skated on for years. It could be my imagination, but I have the feeling that a lot of media folks feel kind of bad about the two-term honeymoon they gave Slick Willie and they've decided to make it up by being aggressively fair when it comes to George and Al. There really seems to be a lack of bias in the way that the 2000 race is being handled (well, except for a few little boo-boos during the convention coverage).
This, I think, is the bad luck of Al Gore: it's not that the people tend so much to tar him with the same brush as Clinton, it's that the media does. He had the bad luck to follow a real stinker who repeatedly farted in the media's hot tub.