It is not exactly news to anyone that Katy Perry is a very variable live singer, like Rihanna. You do have to give them both points for attempting it rather than doing a Britney and lip synching all the time, still they could both do with some extensive vocal coaching. KP does seem a little worse than usual here though and I would imagine her fans would prefer she concentrating on singing rather than that half-assed thing she calls dancing ;o)