There are tons of arguments that the stimulus helped slow the recession and start the turn around.
In early 2009, every indication was that the economy was headed over the edge of a cliff. But at the last second, the country swerved away from the edge and started heading back in the right direction.
Now maybe it was just pure coincidence that the turnaround began at almost the exact same moment that the stimulus started. It could be possible that that the economy began to grow again, job losses began to slow and layoffs started coming back down to earth all at nearly the same time -- right after the president signed the Recovery Act -- and it had nothing at all to do with the stimulus.
More likely, of course, is that the myriad independent economists -- from the Congressional Budget Office to Moody's.com to Macro Economic Advisors -- are right.