I agree with the charity ride idea. my only experience in riding with a group (more than 2) was at a 2 day charity ride and in the begining you see every type of bike known to man, after about 20 miles you are seperated into where you belong and it in turn is really good practice (assuming you can control yourself) for joining pacelines and such with no stings attached.

People initially gave the hybrid i was riding alot of looks, but then all the people with the expensive bikes enjoy the draft you give by being big and upright on a hybrid after about 50 miles of proving you can keep up. I only enjoyed one silghtly derogetory comment about my "mountain bike".

also now is the right time of the year to join. if you wait a few weeks everyone will be fit and trying to catch up in fitness level will be difficult. (this is assuming you live some place with seasons, and the current one is cold)