However the "can't survive contact with real humans" is spot on. One thing you left out as I understand it is that you're supposed to pay back the money you borrowed after the economy recovers. This of course never happens.
True, some countries do decide to seriously pay back debt, I understand Canada did a lot not too long ago, and we paid back a lot of our WWII debt, but those are not the same thing.
And countries that run their operating budgets on ever increasing debt inevitably renege on it one way or another (getting conquered was not uncommon in times past), with I suspect the recent technology based boom (say the post-WWII one) being a special case of the game being able to last a lot longer than normal. (I.e. that's our (the hackers) fault :-).
This is where I say that even Keynes could tell you this stimulus would fail. For instance, there is a local road that even as I type is being "repaired" with stimulus money. But it didn't need repair. Where a $1 of stimulus here is supposed to produce, say, $1.20 in "stimulative value", now we're only getting the $0.20 in value. That's not stimulus. That's actively worse than letting the funds sit there, actively worse than the worse case that Keynes fears; now you're destroying capital. Not only does that not help avert the worst case, you actively bring it closer! And this is the "good" part of the stimulus that is actually infrastructure, too.
Granted, not every project wastes %100 of the capital, but an analysis of the actual stimulus shows the vast bulk of it does; most of it essentially puts useless and wealth-destroying institutions on life support so they can continue destroying wealth. You don't have to guess what the resulting consequences are, you just have to look around.
As an Austrian I believe (with some reason) that a central government is not capable of deciding which projects are actually valuable, any more than a central authority can set prices of any other kind. Moreover, in a relatively efficient economy (it doesn't have to be perfectly efficient), the big infrastructure wins would already have been built, leaving only the dregs behind, things that weren't already built because the economy has decided they aren't of value.
So I think right at the heart of Keynesian economic policy is an enormous "... and magic happens here...", right where the stimulating government entity determines how to allocate the stimulation. Which, if you note, rather precisely and correct predicts how the stimulus fails in the real world, which is that it was very inefficiently applied regardless of whose standards you apply, Keynes or otherwise. A Keynesian must believe that this was a poor application of the stimulus concept, but that hypothetically a government usually gets it right, despite my inability to come up with examples of said; an Austrian like me gets to continue believing that governments are foundationally and structurally incapable of efficient allocation of resources.
That said, my family and I have used CCC infrastructure out in the west in times past. Good investment? Don't know, we were vacationing.
A relevant example this many decades in the future? I seriously doubt it, as you note in your comment on dregs. Which is I gather a lot of what happened in Japan in the last two decades: they've now got some really super-duper infrastructure all over for a steadily aging and decreasing population (peaked in 2006 and is now accelerating downwards: http://en.wikipedia.org/wiki/Demographics_of_Japan#Populatio...).
Nice to see someone else say that for once. If one reads up on what Keynes considers "stimulus" and compare that to what our politicians have labelled "stimulus", less than 10% or so of our "stimulus" was Keynesian. There's a bit of play in that number depending on exactly how you apply definitions, but you certainly can't get it to 80% or 90%.
I am fairly Austrian and consider Keynesian economics to be interesting but misguided on some fundamental points, but in all honestly I can't consider the utter failure of this stimulus as evidence against Keynesian economics. From what I can tell, he too would have predicted this to be utter failure, so both true Keynesianism and my preferred systems predict utter failure and therefore I can't use this to distinguish the two. I am however coming to view Keynesian economics in much the same way I view Communism, as beautiful theories that can't survive contact with real humans. It's too easy for the government to squint at Keynesianism and see nothing but "Hey, spend more money and take more power!", which is not an accurate reflection of Keynesianism at all, but it's what they see. (There's a kernel of truth to that simplification, but no more; the reality of the theory is considerably more nuanced and complicated.)