I didn't find any of the musical performances particularly motivating or all that interesting. The main issue with musical performances at an event like the Super Bowl is that the producers try to cram so many diverse musical acts in a rather short period of time that no performer can make any kind of impact. They only perform shortened versions of songs before the focus shifts, and then usually to a different style of music. As a result, the pacing is uneven and the overall feel doesn't flow.

Aerosmith -- If there was more of a pre-game show, I didn't see any of it. These guys sounded okay as they went through a medley of their songs (as well as a one or two blues songs), but man, they are starting to look their age. Joe Perry should have kept his hair long; it's a better look for him.
Josh Groban -- He performed a truncated version of one of his songs to honor the members of NASA space shuttle Columbia. It's the first time I've ever heard him sing. I think that he was lip-synching, but he sounded okay.
Beyonce -- She sang the national anthem. Singing-wise, she hit all the notes, but her performance would have been much more apropos at some Destiny's Child concert than at the Super Bowl. She did some small gyrations, hand waving and the usual vocal flip-flops of the Britney set. I suppose you can dress her up, but she's still a teeny bopper singer.
Jessica Simpson -- What did she do to earn a credit other than scream "Houston, choose to party!" Minute thirteen and counting...
Janet Jackson -- Very produced and heavily choreographed. Again I suspect lip-synching since her voice never flagged, no matter what dance move she was doing or how her mouth was facing in relation to her headset mike. After Kid Rock, the focus returned to Janet as she reprised Rhythm Nation, both the music and dance steps from the video, for some reason. After the song, she went to a breakdown with a drumline — easily the best part of her act.
P. Diddy -- Didn't do all that much in the first three seconds he rapped. Came back just for a bit after Nelly's Hot In Here.
Nelly -- He did the "Hot In Herre". Clearly lip synching — he dropped the mike away from his mouth at the end of his first verse and the words still came flowin' on.
Kid Rock -- Thankfully, he is clearly not lip synching; the vocal line matched his exertions. He did the first verse from Bawitdaba as well as the initial verse and chorus from Cowboy
Justin Timberlake -- Came out after Janet's Rhythm Nation, did his Rock Your Body tune. Also did a lot of close freaky dancing with Ms. Jackson — possibly a little dig directed towards Britney?

-- Update --
Apparently, Janet and Justin also had a little pseudo-nudity during their act that I just completely missed. Probably because I was more listening than watching. It's kind of sad when you have to do pull those kind of stunts to get sales.

-- Update 2 --
A reader has pointed out to me that I made an error. Joe Perry plays guitar for Aerosmith. Steve Perry sang for Journey. My apologies.