I've always had dubious feelings concerning the world-wide bicycle advocacy ride known as Critical Mass - a large gathering of cyclists that commandeers a city's streets for an evening on the last friday of every month. The idea is to assert the presence of bicycles as rightful, legal vehicles.
Now, I'm a former messenger and still bike everywhere. Most car drivers drive me nuts. But I'm not so sure the best way to coexist is to drive them nuts right back.
In an entirely more subtle, and I would argue more personally engaging manner, Seattle's Ghostcycle.org started marking the sites of bicycle/car accidents with entirely white painted bicycles and placards reading, "A cyclist was struck here". Each placard is numbered, so you can read more on Ghostcycle's site about each accident. What's more, a Google map pinpoints all reported bike accidents in the city, not just those marked with a ghostcycle, and includes accident stats and bike advocacy resources.