The report has not come out, yet. Gen Petraeus will be in DC on Sept. 17, to present it. Pelosi and the Dems are trying to poison the water with negativity about the report, so that when it DOES come out, people will be loathe to believe that it has any positive news at all, and if it does, it's because the General and the President are lying about Iraq. The Dems see this as a last ditch effort to keep the moonbats happy, because if the news IS good, the American people might just start distrusting the Dems and their continual whining about the war, and that would not be good, politically, for the Dems in the 2008 elections.
For Reid, Pelosi and the Dems, it's all about THEM keeping Congress and winning back the White House.