Either way, this doesn't appear to be a well organized event... I say that because:

1)the wiring was "amateurish"
2) there do not appear to be multiple bombs planned (at least not yet)
and
3) the fireworks were not concealed in the car, which led to the street vendor noticing it

This strikes me as someone (or some group) who does not have a lot of experience with car bombs. Any of those changes would have made this attack more successful (in the sense that it would have "created more terror".)

I don't think it would shock anyone here if this IS set by an Islamic group. However, my gut says (based on very minor evidence) that this is the work of a splinter group/individual, more likely inspired by, (but not directly connected to) some radical group. (Islam or other)

In this case "inspired by" means: may have connected to someone by the internet, but no personal contact/teaching.

Bill Roggio's Long War Journal reports that a Paki-Taliban leader has put out an audio recording claiming credit and it was posted before the event, lending some credibility. That doesn't necessarily mean we have Talibunnies running around NYC, but if verified it would mean that there is a viable communications channel between them and whoever here attempted the bombing, which is bad enough itself.

I heard about the Pakistani Taliban claiming credit, but I'm skeptical for at least two reasons.

First, they haven't ever (to my knowledge) shown any inclination toward being a group with global reach. Or even with regional reach. They are, I though, a pretty local phenomenon.

Second, while the group does have some experience with car bombs (having used them extensively in the past) this looks like a car bomb put together by someone who has never put a car bomb together.

I suppose the one can explain the other, but I'm going to be skeptical for a while.

Even if the Pakistani Taliban was not involved in the attempted car bombing (as is possible, and perhaps likely), the fact that the organization is attempting to claim credit for the near miss indicates that they want others to see their sites are no longer just trained on Islamabad and Kabul. And that might speak volumes about the planned evolution of their future strategy and tactics.

OK, someone with more tech background than I have can fill some details in, but to my untutored eye, to me this not only looks like the work of someone who's never actually built a working explosive device before, but like the work of someone who's learned all he knows about IED's from watching movies.

That the triggering "clock" shown in the wire-service photos looks large enough to be something taken off Flavor Flav's neck, or from a nursery wall, is the first thing that caught my eye. The fertilizer was wrong, we're now told; probably should be thankful they weren't trying to blow stuff up with steer manure.

Which brings me to the technical question about that propane can stuff; don't you have to do that in a confined space, so you can get air-fuel mixing? Least that's what I remember from the movie...