Cagewriter has the story on Yahoo.com:
After plenty of speculation that the UFC may bail from its May 1 date for UFC 113, the promotion has decided to push the event back a week. The reason? It's all but a certainty that Floyd Mayweather and Shane Mosley will meet in Las Vegas on May 1. The UFC does not want to go head-to-head against a powerhouse boxing pay-per-view.
This afternoon, a UFC source told Cagewriter that UFC 113 was headed for May 8. This evening UFC president Dana White confirmed the date change. The switch was made possible when the Bell Centre was able to move a May 8 concert.
“We were trying to not go the same night as boxing but these [expletive] guys can't get out of their own way,” White told Cagewriter. “I have never seen anything so unorganized, selfish and dysfunctional as boxing. It's a joke!”