I think Bono is great in music videos, but he has said he will not do movies because he thinks he is a horrible actor. He looks very embarassed when asked about Entropy in interviews. This is probably why he chickened out at the last minute on playing the crazy art dealer in Million Dollar Hotel. Wim Wenders got annoyed and casted a guy to do an imitation of Bono in the role. He even wanted his 1/2 second cameo cut out, saying something like "oh look, pop star shows up in own film". But Wim put his foot down and left it in anyway. I think Wim talks about this in the director's commentary on the dvd.
And to fill in those who haven't heard about it, Bono really was asked to play MacPhisto in a Batman movie. He was friends with the director, and Arnold Schwartzenegger was threatening to leave the film at the last minute. The director was desperately trying to line up a potential replacement that could attract an audience. Bono agreed to step in if needed, but Ah-nold stayed in, which is our loss. Normally I would cringe at the thought of making up a new Batman character for purely commercial reasons, but I would make exceptions for MacPhisto...
I'm not sure if Bono could play normal people in a movie without a lot of coaching, but he can certainly play whacky versions of himself, like MacPhisto or Mirrorball Man. You know what though? I think he would be great playing an Irish Catholic priest a la George Carlin in Dogma...