Tax cut for investments...Can this really stimulate our economy now?

Tonight in the Republican response to Obama’s speech, I heard again a mantra that I also heard from the new Republican National Committee Chairman that we need to give tax breaks to encourage investment and that this would do more to spur the economy than government spending.

Okay, so here’s my question: When demand is dropping like a rock, what exactly is supposed to possess a businessman to invest to increase his capacity or what have you? Is there any economist out there who has a coherent argument of how this sort of supply-side approach will really work in our current economic predicament?

Can’t speak for any economists, but business journalist Kent Hoover puts forth this description of business tax incentives in the stimulus package: