World War 2 brought us out of the Depression. There was a boom immediately after World War 1. During the Vietnam War, the 60's were a time of prosperity - which, coincidentally, tanked when we started pulling out. (Yes, I know the oil embargo had a lot to do with that... but hmmm.....)

$40 billion is not empty spending, as I saw someone else say. Every dollar spent goes to someone even if it is spent for munitions, fuel, training, transportation, or whatever. The $40 billion earmarked so far won't have nearly the bad effect envisioned by some.

Furthermore, you have to remember that we are (supposedly) still running a surplus, even if it is a lesser surplus than originally projected.

I think the biggest economic impact will still be the shattering of the World Trade Center; figuring out how that will effect the economy is near impossible.