I was reading a preview article of Obama's speech on CNN a few days ago. I can't find the article anymore, but it it had an interview with a small business owner about potential payroll tax cut, and the owner said (paraphrasing), "tax cuts aren't going to provide an incentive to hire people that I don't need."
That quote basically describes the story of the economy today. US Real GDP is a mere fraction of a percent away from the all-time high in 2007 and growing, yet the economy has 7 million fewer workers. And that jobs figure isn't even counting the jobs that would have to be added to keep up with population growth.
We have millions of workers providing no value, or even negative value, to the market. No amount of stimulus is going to fix this. Sure, stimulus funds could employ some of these people for a while, but chances are good that they will find themselves right back in the unemployment line once stimulus funds run out.