Foursquare, the rapidly-growing social networking service through which people check in at any number of locations, apparently had a pretty good year in 2010 — and it’s no shock (at least to us) that D.C. was a big part of that success. According to an infographic posted on the service’s blog today, Washington was the site of the service’s single biggest check-in event (last October’s Rally to Restore Sanity and/or Fear, where 30,525 people checked…

This morning, we asked a couple of questions about Metro’s record-breaking Saturday — namely: what were Metro’s criteria for estimating the expected crowds, and how high the ridership could have gotten if the trains had been running more frequently. WTOP’s Adam Tuss and TBD’s Dave Jamieson both do us a solid and deliver the answer to the first question — and found that the rally organizers were the ones to blame for us not knowing…