Welcome. Sorry that the bike thieves got your Haro. May it be replaced in your stable soon.
Commuting becomes easier when you really learn your way around… what streets to avoid and which ones get you where you want to go. Arlington, Fairfax, Alexandria and Washington DC all have pretty good maps of cycling routes. They help, but are not the end-all. There are plenty of good routes out there. Find a balance between your sense of adventure and self-preservation and hit the town to explore. This ends up being a pretty good place to ride.
Mountain biking is also very abundant. There are some good local resources to help you with that. Down South there is the Cycling Central Virginia group: http://www.cyclingcentralva.org/forums/
Closer to home is the Mid Atlantic Off Road Enthusiasts (aka MORE): http://www.more-mtb.org/
A significantly less reverent (and personally, more down to earth) group can be found at Log-off Ride-on (aka LoRo): http://www.logoffrideon.com/forum/index.php?action=forum
All three groups have very active groups that ride often. There are lots of good resources on where to ride and what to expect.
Hope that helps.
Pete
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