Last year things got extra hot when Katy Perry sang with Elmo on Sesame Street. Parents went nuts at her revealing outfit. The footage never aired on the show, but ended up being a major smash on Youtube.
http://www.youtube.com/watch?v=YHROHJlU_Ng
After a screening of Being Elmo at the Full Frame Documentary Film Festival in Durham, NC, Elmo and his pal Kevin Clash revealed that Katy Perry will return to the show for a second try.
No news on when this event shall take place, but it seems Elmo was hinting to the song choice.