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.
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...