Germantown to DC: yes, I'd take the railroad
The Sunday Washington Post Dr. Gridlock column has a letter from a Germantown resident complaining about the cost and time it takes to ride the subway from the outermost Red Line station at Shady Grove into Montgomery County versus taking the MARC passenger train service.
It's about 33 miles to Downtown DC from Germantown. It still takes an hour by train, but is cheaper and a lot more comfortable.
Definitely for trips of that length, if you have the option of a railroad trip vs. a heavy rail trip, I'd take the train.
It would be nice to have more railroad transportation options in the metropolitan area and region, for one contra-flow service on the Brunswick Line would allow residents in the core to take the train to Rockville, Gaithersburg, Germantown, and Frederick during the day. (Note that historically this kind of service was not provided on the line, at least over the course of the last 50 years, and probably before that.)
I do know of at least one person who takes the VRE from Alexandria to DC, rather than take Metrorail.