Cynthia Estlund (employment and labor law) at Columbia Law School has accepted the senior offer from New York University School of Law. She is the second senior faculty member to decamp to NYU in roughly the last year. One additional senior Columbia Law School faculty member is also entertaining an offer from NYU at the time of this writing.
UPDATE: A Columbia professor writes to call me on my careless use of language: "Just to point out that the American Heritage dictionary, found at dictionary.com, defines 'decamp' as 'to depart secretly or suddenly.' Since Cindy got her offer a year ago, has been visiting at NYU this semester, and the AALS deadline is in two weeks, I'm not sure the characterization is accurate."