Yes, it'll be busy, what with all the long-weekend visitors plus Memorial Day events like the annual Rolling Thunder gathering (that said, Rolling Thunder's an educational event in and of itself, with tens of thousands of Harley-riding vets roaring into town to honor their fallen comrades). Honestly, though, DC stays pretty continually busy until school's back in session after Labor Day. Come midweek if you can, or try another weekend (surprisingly enough, weekend hotel rates tend to be lower as that's when the politicians, lobbyists, and conventioneers are out of town).