This may be old hat to some of you, but I've recently become a big fan of the Census bureau's Census Explorer for getting a quick overview of the numbers and per capita percentage of bicycle commuters in a given area before using American Factfinder to get a more complete picture. The good things about Census Explorer is the ease and speed, and the map with figures overlaid. Every time I've applied it to Georgia on a particular topic I've come up with surprises. For instance, when I was looking at foreign born population, in addition to the obvious concentrations (Gwinnett and Dekalb counties), a north Georgia county on the Tennessee line (Whitfield) has one of the heaviest concentrations of foreign born residents in the state.
Applied to cycle commuting, here in Georgia, the counties and census tracts with higher than average bike commuting were very surprising to me, with the exception of Clarke County, where UGA drives the numbers up. Chattahoochee, Appling, and Baldwin counties all had higher than average per capita bike commuting. An even bigger surprise to me was that, at the census tract level, Clayton County wins the prize, with a census tract where bike commuting gets over 10% of the commute share. I haven't dug into the numbers yet, but I suspect the absence of MARTA in a county with a large number of low income people pushes that number up.
I've decribed the simple steps for quickly pulling up a map in a post at Atlanta Larry.