I do. Ten minute drive to the Metro. Long term parking at Metro for $4.75 for as long as I want (free if i come home on a weekend). Then 20 minute Metro ride to National.
Definitely beats a 40 min drive and $10/day parking at Dulles and then waiting in the parking lot for a shuttle to come by and pick you up.
I think the better question is "Why would anyone choose Dulles over National?"
Does anyone even fly out of National?