We went and saw Bruno last night. Peter liked it much better than I did. I'm not against it reflexively--some of the viler participants really did seem to deserve what they got. But overall, it just wasn't that funny.
Partly that's because Baron-Cohen's schtick is wearing a little thin. Yes, you've proven that if you put people in weird situations, they will usually go along to be polite. But the sight of normal people awkwardly complying with Cohen's antics seems less amusing than it did five years ago.
But I suspect that the deeper problem is that most Americans just aren't as openly homophobic as he and director Larry Charles were clearly expecting. Baron-Cohen is funniest when he gets one of two reactions: genuinely horrible people say genuinely horrible things, or he gets people to go along with his non-horrible, but utterly surreal questions.
But there's little of the former, and almost nothing of the latter, which is what's always charmed me about him. They are forced to resort to provoking people by being complete jerks: fondling people inappropriately, showing them "surprise" sexually explicit video, and if all else fails, grabbing their stuff. And the responses to people being complete jerks are not particularly surprising or interesting, and therefore, not really very funny.