on PBS and in the interview afterwards, he mentioned that they hadn't practiced, they were sort of winging - or ad-libbing it (it was a full orchestra, but he was the focus (again, I apologize for not remembering the particulars, because I'd love to remember it).
He FELT the music, he became it, it was so astounding it's sort of hard to describe. I've seen him at Lincoln Center and SPAC (I think it was SPAC - maybe Tanglewood) in the past, but this performance - even though it was not live but televised, was just incredible.
About the piece he and Perlmann (sp?) played that was written for the inauguration by Williams, I think - is there anyone else that thinks it was partly based on Stevie Wonders' singing "Ba-rack O-bah-ah-ma" almost in a scale progression, a couple of times during the primary or general election events. I would love to know that it is... it sounds like the notes are the same to me.... (if I find a clip of Stevie singing this, I'll add it in an edit).
here: Just the part where he sings "Barack Obama":
http://www.youtube.com/watch?v=guCcgfVUeZk It would just be a lovely way of honoring him in such a beautiful piece and performance...