The following is a reasonable summary, in my view, of the available evidence on the impacts of discretionary fiscal and monetary policy actions taken before, during, and after the recent financial crisis:
Posner shows, among other things, the basic impossibility of doubling US exports during the next five years. I consider whether such a policy makes sense, even if it could be achieved. My short answer is that it does not.
With the one year anniversary of the signing of the stimulus it is useful to review the facts and data as they came in during the year. Here are the relevant posts from Economics One. Most look at actual data and find virtually no impact.