No offense intended - I'm an American citizen so I don't have tons of room to talk!
PIGS is an acronym - it just makes it easy to remember. That's the only reason I can name all 5 countries. No one things that citizens of those 5 countries are swine, just like they don't think that citizens of the booming BRIC countries (Brazil, Russia, India, China) are dumb.
Not so much in Dublin perhaps, but rural Ireland is all about favours and bartering, it's not even really a "black market" since cash isn't the currency.
I dunno, it's cool, it makes it feel much more like a connected community, but you can't trade mackerel for fenceposts (this is a real deal in which I was involved) in the global economy without going via actual cash...
From what I've read about Greece, Ireland's problems are completely different. Nothing to do with a black market, more to do with an incompetent government that let property prices get out of control.