 Leno celebrated by devoting an entire monologue to Michael Jackson jokes.Because Leno's show continued to lead all late-night programming in the Nielsen ratings, the pending expiration of Leno's contract led to speculation about whether he would become a late-night host for another network after his commitment to NBC expired.Leno left "The Tonight Show" on Friday, May 29, 2009, and Conan O'Brien took over on June 1, 2009.