I've been on a couple cm rides in Pittsburgh, and think its a great thing... Its nice to see such a mixed group of people getting together to ride, and show that there is a desire for a more bike friendly city.
That being said, I do agree that there are some problems with CM, mainly keeping the scope of the ride on bicycling issues. I heard too many 'no more war' shouts during the ride. This is not productive towards bike awareness. I'm sure many people saw the riders and heard the shouts and figured it was an anti war ride.
As long as the rides stays 'on topic', I am in support of CM.