5 days in DC!!
Well try ethiopian cuisine. You'll find it a wonderful treat and Meskerum in Adams Morgan has a fun atmosphere. You can sit tableside or upstairs you can eat sitting on little floor stools around a large copper plate. A unique cuisine that does not get enough attention. Enjoy the flavors. This resturant has had some great reviews too. I hope you check it out.
Cafe Milano, right off Wisconsin Ave, might have the "happening vibe" you're looking for. It's pretty popular among the politcal/diplomatic crowd. Another great choice in Georgetown for a special occasion is Citronelle, located on M St. in the Latham Hotel.
There are a lot of mediocre touristy restaurants in Georgetown, so be careful.
If you happen to find yourself in the Dupont Circle area, I recommend Pecse for really great seafood and Obelisk, which has a pris fixe Italian menu, both on P Street east of Georgetown.
In my opinion, the hot restaurant in town right now is Komi, which has a Greek/Mediterranean menu, on 17th St. between P and Q streets.
Enjoy your stay in DC.