As happy as I am to be heading to GW in the fall, I have to agree with the others here suzie. If you were set or near set on BU, don't let one ranking change switch you. I assure you, its not going to affect BUs recruitment, nor will it affect GWs.
US News has to change how they rank schools enough each year to illustrate various subtle and some not so subtle changes. By doing this, they assure that people will go out and buy their magazine (or at least pirate it off of xoxo)