As part of the advocacy for the stimulus plan that the Obama Administration proposed and signed in the first weeks of his presidency, the Obama economists provided a forecast of what the economy would do with and without the stimulus. For a summary, see this graph.
With the unemployment figures for April at 8.9%, it appears that we are not on the track that was projected for what would happen with the stimulus plan, but rather on the track that was projected for what would happen without it. In fact, it appears that we may be above the unemployment rates that were projected if we did not pass the stimulus plan.
If this pattern continues, will be able to say that the stimulus failed? Unfortunately, we probably will never be able to really tell what effect, for good or for bad, the stimulus spending actually had.