Congressional Budget Office on the stimulus bill:

In contrast to its positive near-term macroeconomic effects, the legislation would reduce output slightly in the long run, CBO estimates, as would other similar proposals. The principal channel for this effect is that the legislation would result in an increase in government debt. To the extent that people hold their wealth as government bonds rather than in a form that can be used to finance private investment, the increased debt would tend to reduce the stock of productive private capital. In economic parlance, the debt would “crowd out” private investment. (Crowding out is unlikely to occur in the short run under current conditions, because must firms are lowering investment in response to reduced demand, which stimulus can offset in part.) CBO’s basic assumption is that, in the long run, each dollar of additional debt crowds out about a third of a dollar’s worth of private domestic capital (with the remainder of the rise in debt offset by increases in private saving and inflows of foreign capital).