Ke$ha was obviously singing and not lip syncing (there was no evidence of the high notes from the backtrack), and Pitbull most likely did lip sync, but apparently all rappers do that.
I wasn't so much disappointed, but I really wish that she'd gone for some of those high notes and not worried so much about the "oohs", because people are just going to think that she can't sing live from that.

I wonder if she chose not to, or was told not to? Either way, it left me wanting more.
She looked great though, and the official video SLAYS, so I can forgive this otherwise average performance. It wasn't bad, it just wasn't anything special either.