Pop superstar Katy Perry has been tapped to host "Saturday Night Live" on December 10th, with iconic Swedish singer Robyn serving as the musical guest,a role Perry herself filled the first time she appeared on the show, last fall.  Perry also appeared on the show as the musical guest earlier last year.  Perry also appeared in a series of episodes of "How I Met your Mother" last season, and provided the voice for Smurfette in the recent box office hit, "The Smurfs."