Stayed here one night on my way home via the train/Amtrak through Reagan National. Except for a little traffic it was really convenient and was a really nice stay. It is located in the Carlyle area which has high end tower residences and the courthouse...and the King St Metro station. What limited contact I had with the front desk was excellent... pleasant service as one expects from Westin properties.
I called them from the train station to have the shuttle pick me up. It took 45 minutes because of an accident near Old Town but otherwise it was a pretty quick trip 5-10 mins from the train station. The hotel is only a couple of blocks away from the Metro... an easy walk during the day when you can take the pedestrian underpass. But the underpass is closed at 9pm so when I came back late after a Nationals game, I had to cross the street... not bad when traffic is light.
It is not too close to the main tourist areas of King Street in Old Town but still walkable; they do have a shuttle that can take you there.
I had an early flight out on a Saturday and a cab to Reagan was $20 (w/ tip).