I live in Reston VA. (Suburbs outside of DC). The Metro works nicely for me, there is a park & ride that has an express bus straight to the Metro station. (I could ride a bike there, but I work in a suit & tie every day). It makes the commute about 15 min longer, but far more enjoyable. Parking (alone) would run me $24/day. For weekday commuting, train & bus wins by a long shot.
In addition, the last two firms I've worked for have offered a private bus from the train straight to the office. I think this should be a required benefit for companies that call themselves "green".
The city of Reston is great about having sidewalks and paths. Many of them do not run next to the road and provide a great way to walk places on the weekend without sucking down exhaust fumes. I hated suburban living before I moved here, but I think they really provide the best of both worlds.
"Consistency requires you to be as ignorant today as you were a year ago." -- Bernard Berenson