I think the answer is kind of implied in your own question there Ag-ness. Repercussions will be highly localised across the globe and more so in a diverse region such as Europe. I think Europeans are already retreating within their own borders and even within their own regions in a sort of centripetal movement contrary to the whole openess of the EU ideal. The borders are historically pretty fluid within Europe and moreso with the current Schengen Agreement, but it is actually culturally extremely fragmented and tightknit, which is to say, even people within the same country treat their countrymen as foreigners even though, in physical terms, they don't live that far away from each other. This is expressed primarily through language variations and visual differences (ethnicity) and secondarily through cultural paraphernalia: clothes, styles, food, housing, etc. I expect a pretty firm backlash against foreigners. If major parties around Europe fail to address the "alien" question in their borders then far right demagogues could rise up. But I don't see it as particularly likely given how far right from centre major parties are in most major European countries. Sure there are rumblings in Austria, Sweden, Germany, etc. But they will remain that. YMMV with smaller countries though.
When you look at Europe economically you can pick out all the cream pretty easily. If you get a map of Western Europe and start drawing circles around the most economically viable areas you'll find they are all pretty easy to identify and all clumped together. Wealth is really very centralised there, as is the case most places globally. Disparity has increased alarmingly over the past decades, although Europe has not been as extreme as some other places. Beyond that cream, there is a lot of deadweight in Europe. 500 million odd people, most just clinging to the side of economic region trying to live of the fat of the beast. That economic baggage is getting squeezed already and it will get worse as those with power and wealth tighten ranks in the face of the ongoing economic onslaught. Will that result in the mayhem in the streets you suggested? Quite likely it will I think. But again, as with Greece, it will be localised and mostly people will go on about their business, though in a significantly diminished economic capacity. Re. the Euro question - currencies come and go, it's not the end of the world. I think the Euro will be redefined not scrapped, but at that point it'll all be about semanatics and face saving. It will not survive in its current form, just as the EU will not as a whole. The Schengen Argeement has now been broken by core countries like France and Sweden. The crumble has begun.
I always said the deathknell for the EU project was December 31st 2007 when a host of Eastern European countries were introduced into the Schengen pact. You can't have open movement with that kind of economic disparity. Romania and Germany are just a few hours apart by car, but they are worlds apart economically. Places like the border between Austria and Hungary are where the whole problem of the EU plan have come to a head. Vienna is spitting distance from a vastly different world in provincial Hungary and yet they are meant to act as a single economic entity. The result is widespread criminality and dissatisfaction. Relative wealth disparity is enormous. Although there is clearly positive transfer of wealth and cultural interaction, this only functions somewhat gracefully in times of economic expansion.
I doubt the general trends I outlined will be significantly different in places outside Europe, but how they manifest themselves specifically will vary greatly. Australia is a much more uniform and homogeneous place than Europe so it's probably easier to successfully describe trends relevant to many as has been done on silverstackers at length.
Anyway I cannot start dialogue on this as I get a bit frazzled, peace to all
