William Ackman's long standing short on the monolines is expressed again in detail at the recent Hudson Institute Presentation. (You need to register to see this, but it is free to do so and well worth the effort.) He has made many public presentations on the faulty business model of the monoline insurers. One of which was the Ira Sohn Conference in May, 2007.
Below is a cut from the panel discussion following the formal presentation at the Hudson Institute.