Certainly the stimulus act didn't work as hoped - the economy is not booming, and unemployment remains very high. On the other hand, the economy has grown, just not as fast as hoped. Economists on the left and right are both arguing that each other's policies don't work. (The conservative view being that any regulation of economic markets, AT ALL, will slow the economy, and so government ought to have in essence, no economic policy at all, as well as the lowest possible taxes.)
It seems to me that the right's laissez faire canards are ill-conceived and largely created the collapse in the first place. But that doesn't necessarily mean that Keynes was right, and increased spending along with increased taxes are the cure. Given that we went from an economy that was flush and a budget surplus (Clinton) - to a Republican-controlled house, Senate and White House - and then right back to a Democrat controlled house, Senate and White House, there should be some fairly persuasive data when all is said and done.
So yeah, this should be interesting.