We just had an earthquake, first time I've been through one. Strong enough to knock a few books off a bookshelf (they were piled high). My guess is it lasted 20 seconds or so--we'll see what USGS says since they're based in Reston.
[Update: 5.9 apparently and the first of that magnitude in Virginia for a while. One of our cats slunk down to the basement, very upset, while the other on our bed opened an eye and went back to sleep. Actually, I don't know that for sure, but she was still in her position about 5 minutes after the earthquake. Different strokes for different folks and different cats.]