From a story in the latest Rock & Rap Confidential (not on the Web yet, alas):
At June's Technology Entertainment and Design conference in Tanzania, Andrew Mwenda, a Ugandan journalist and social worker, spoke out against reliance on foreign charity, pointing out that it had never succeeded in reviving an economy anywhere in the world, least of all Africa. He made his points only with difficulty however because throughout the speech he was heckled from the back of the room with shouts of "Bullshit!" and "Bollocks!" The heckler was Bono.
More on Bono's switch from headliner to heckler here.