I have lived in Frederick County (near Brunswick, the largest MARC stop on the Brunswick Line) for 7 years and my husband has commuted to Capitol Hill/Union Station the whole time on MARC. From Brunswick to Union Station is a 90 minute ride. My husband also drives in to the Hill at least once a week, on Tuesdays, and in rush hour traffic it's about a 90-120 minute commute. (20 minutes of that is actually just getting to the city of Frederick from our house near Brunswick). The best driving route to the Nats stadium area is down I-270, across the Legion Bridge to the GW Parkway, then across the 14th St bridge. That's the route my husband and I take to the Hill. There are commuter buses that go all the way into DC from out here, but they don't have as many timing options as MARC does.
Also, Frederick is growing by leaps and bounds. In the 2010 census, the state of MD grew by 9%. Frederick County grew by 25%!! There are a lot of people moving to Frederick from the metro DC area because it's a much easier life out here (that's why WE did it!). I'm a Realtor licensed in MD, DC and VA and I still do a lot of work in DC (I worked on the Hill myself when we first moved out here) and we have never regretted the move. Plus, when we want to go somewhere on the weekends, no traffic!
FYI: Cost of living out here is a lot better too. Daycare alone was worth the move.