I work near the Capitol. Your last few blocks of the commute suck because of traffic (both cars and pedestrians) and the potholes from the roads.
The riding outside of town is excellent. I mentioned in another thread that suburban Maryland maybe 20 miles east of town is some of the best riding anywhere. You can ride on miles of scenic country roads along or near the Cheaspeake Bay and the rounte combinations are so numerous, you never seem bored.
Potomac Peddlers is a 5,000 member club with multiple rides every weekend day. They are for all distances and speeds. If you race, there are maybe four local teams and lots of other racers that do group training rides.
There are some semi-organized tris. One local propmotor of tris quit so many of the more formal racesare covered now by a NC firm. Consequently more now are located in the southern end of the area.
In nothern Viriginia you can't beat Bonzai for a tri shop. Two Arlington shops that are good are Spokes and Revolution