Actually I have read that there is a sect in Iran who actually do believe W is the 12th Mahdi, who will come and destroy the corruption and evil in Islam.
That was a bunch of college students tossing that idea around when W invaded Iraq. They hoped he'd come to Iran next and clean things up. They were spoofing on the beliefs of their elders at the same time, I think.
BTW, the Shi'ites believe the Mahdi will be the return of the hidden 12th Imam. The Sunni's believe he will just be a great Muslim born recently.