Cycling census

How many of us are there really? I've wondered this for at least a couple of years as I've watched other cyclists when I'm on the road. But when I'm on a bike or in a car keeping track of how many cyclists I see is usually a dangerous proposition. So I have two questions: 1) what is the best method for counting cyclists and inferring a larger total from that and 2) what's (or is there a) the best way to do that from a bike? My guess on No. 1 would be something akin to the Audobon Society's Christmas Bird Count. It would be nice to know who's out for what end — commuting, training, exercise and so on — and where they ride but I'll take a gross number for starters. And I'm happy to start real small, say for Cary or specific areas of western Wake County. I've done a quick and dirty Google search but didn't find much. Please speak up if you know of other such censuses or if you have a neato mosquito sampling method.