IMO, mirrors should be required equipment along with helmets. I would not be able to drive a car without a rearview mirror, and I definately cannot ride on an organized ride with hundreds or thousands of others without knowing when someone was going to pass me. The cyclists who complain about the fast tandems and pace lines are the riders who ride side-by-side (with a 4 foot gap between the pair) at 12 mph and take up the entire lane, rather than ride closer together and on the right side of the road so the quicker cyclists can pass. I pass many people and many people pass me. After about 50 "On your left's", I only announce my passing if I see the cyclist does not have a mirror, or if the cyclist is not riding a straight line (unpredictable), or I'm coming up behind a lone cyclist on a quiet stretch. Just as a driver of an automobile, gives up the passing lane to a faster motorist, the slower cyclists should stick to the right. And after saying all that, with 10,000 cyclists last year, I only ran into the non-movable slow cyclists about 1 - 2 times a day. Nothing to complain of, and I enjoy being part of the show, part of the whole big crowd. There's something for everyone. We just gotta have fun.