I live in the DC area and go to the DC Cherry Blossom Festival every year. It's such a beautiful sight, the trees are in full bloom and you also get a view of Washington historical sites along with the Potomac basin.
It is very crowded though, people from around the country and the world fly in just to see it. Aside from the Japanese cherry trees though, there is not much Japanese about it.
I know they have several events going on during the festival that have some Japanese culture. But, at the site of the blossoms, you get hot dogs, Chinese food and ice cream. But the view is gorgeous and worth the hassle.