Wife's birthday...although she'd like a ride to, so maybe.

The W&OD goes through close to Reston, and heading west puts you out into some nice country. 20 miles out will take you past Leesburg. If you were feeling up to more miles you could go out to Purcellville, which is very nice.

Traffic in the area of Reston can be nasty, so although I'm generally not a big fan of trail riding in particular, that's going to be a busy day in the area due to a lot of people taking a flex day for Friday. I'd kinda suggest doing the trail to someone not familiar with the area, and being a rails-to-trails, it's flat, and stops aren't real frequent once you get out past Herndon.