Arlington’s CommuterPageBlog has an awesome map showing Capital Bikeshare usage. The darker the line, the more trips are made between the two stations that line connects.
The densest concentration of users appears to form a triangle with points at Logan Circle, Dupont Circle, and the Reeves Center at U Street. It will be interesting to see how this changes over time as service is expanded to more neighborhoods.
Cross-posted at BeyondDC.