It's a lot better than most cities but it can be time consuming with all of the stops and changing trains depending on your destination. I think they increased the hours since I lived there, but it also used to close relatively early, so if you were going out at night, you had to either go home early or pay for an expensive cab ride home.
Beats the hell out of Chicago's. I was staying in the suburbs and going into town on a Sunday. I just missed a train so I checked how long until the next one, expecting 20 minutes or whatever. TWO HOURS in between trains!
Yep, they typically shut down at 11. Want to go to a Nats or Wizards or Redskins late game, or go out to a late dinner or party? Yer screwed.