The nonpartisan Congressional Budget Office has done an analysis of the federal economic stimulus package and predicts that while it will result in short-term growth and job creation (over the next year or so), the long term effects will likely include a "crowding out" of private investment, resulting in a lower gross domestic product.
Scanning through the provisions of the bill (which you can see in its entirety at readthestimulus.org) it becomes obvious even to a layperson that much of the spending will not achieve the bill's stated goal of creating jobs and boosting the national economy. While some government spending will inject immediate cash into the system, this plan goes completely overboard, and in the long run could do more harm than good.
Obama defends the largest federal spending bill in US history by saying that we can't repeat the failed policies of the Bush administration, which he says got us into this mess. However, Bush's plan failed because it did not balance tax cuts with corresponding spending reductions. The Bush tax cuts did help the economy, but the benefit was offset by irresponsible spending.
While some of the spending will probably stimulate the economy, the pork in the bill could more than offset the short term benefit by generating massive government debt. Further, Obama pressed congress to pass the bill quickly rather than taking more time to prepare a bill with less flaws. Therefore, it seems to me that Obama is repeating two of the failed policies of his predecessor: 1) reckless spending and 2) rushing to take action, which is worse than no action at all.