Last month the Transportation Research Board's annual meeting in DC included a discussion about hitchhiking, what has happened to it, and the rise of organized car-sharing (i.e. slugging).
The slides from the talk are over on the Freakonomics blog and they make note of how topical this is to the DC area. One program that the discussion mentioned was Virginia's new Real-time Ridesharing Pilot Program that will try to lessen the impact from all the government office re-locations taking place right now. The app-based program is still in early phases, but it hopes to be able to match drivers to passengers and have a micro-payment system that allows both to contribute to the cost of the ride. For the pilot program the goal is to have each participant making twenty ride matches per month.