They seem to be well-loved by ESPN, so I assume they get decent ratings. I also assume that's because it's the only option for a lot of people. As subhead said, their schtick is so contrived it's painful. I usually switch the station whenever they try to pull it off.
Unfortunately, my normal morning radio show got nuked, so I'm stuck with M&M, music or dorks trying to act like they're really hip by making fun of celebrities.