I think it is very hard to define "stimulus," and much of the debate arises from people's interpretation of it.

As far as updating America's ATC systems, I doubt that money will do anything noticeable, but as Ewfflyer puts it, it certainly does put money (however small) where it is desperately needed.

In sort of an odd-way, I suppose this way we can be sure the money goes where it is most needed. For example, if I know I only have $10 for gas this week, I will have to be very conscientious as to where I drive. If I had $100 for gas I may make a few, "less important" trips with my car... just food for though.