First of all, is there any nerd who DIDN'T know about MST3K? I don't think you needed to spend an entire episode telling people about it.
Also the show is not very funny. The thing about feature length movies is that, even for truly ridiculous movies, there is a lot of down time where nothing ridiculous is happening. It's pretty hard to make someone walking down a hallway funny the first time, let alone the 33rd. Even the funny parts are usually funnier just on their own without assistance. I know what I'm seeing is ridiculous, I don't need them to tell me. The few episodes I've watched have each given me a few good chuckles but the doesn't rally justify the 2 HOURS it takes to watch one of these things. Still, it was a good idea and I think the show would have been better served if they just made fun of specific portions of films rather than trying to write comedy for the whole thing, unfunny parts and all.
Also, the I blame the show for creating that-asshole-who-thinks-he's-funny-and-keeps-shouting-unfunny-stuff-during-the-movie that's always there at every group screening I ever attend.