The increased risk that a downgrade represents may push interest rates up in the US - and that could even flow through to the cost of borrowing worldwide.
If that happens (US Treasury is still saying it won't) it will suck cash out of the global economy and an already tardy recovery will slow further.
A slower recovery also means less global demand for commodities and that would hurt New Zealand exporters.
But in the grand scheme of things, three years into this grim economic malaise, it should be just another bump in the road.
The problem is that markets seldom operate rationally at times like these.
Panic sets in and all bets are off - as we saw last week when renewed concerns about European debt sent markets into a hissy fit.
The real threat from this downgrade is that as a symbolic gesture it tips already jumpy markets over the edge. At worst a major meltdown could paralyse the system, like the collapse of Lehman Bros did in 2008. That would be a disaster.
New Zealand's market is tiny by global standards. It would be a stretch to say that some resolve from local investors could change the way the world reacts to this crisis.
But who knows, we may have some influence in Australia. If New Zealand and Australia don't panic, perhaps that will be noticed by investors in Asia and so influence Europe and the US as they open tonight. If fear and panic can spread then perhaps common sense can too. Here's hoping.