I dealt with this crap at two Rock The Bells performances last year, and I'm sure he'll have the same problem when I see him next week at Rock The Bells.
He doesn't even do songs half the time. Much of his set is like "Mos Def's iTunes playlist."
He's just leaving people confused, and bored ("hey, let's go get a beer before Nas comes on.")
Mos can do new songs, sure. But if he's not doing "Umi Says," "Ms. Fat Booty," "Definition," at these shows, he's not going to win the crowd over AT ALL.
(of course, this only applies to Mos Def shows without a band.)