Actually, as I understand it, "euro membership is irrevocable" as long as the nation in question remains an EU member. So to leave the euro Greece would have to withdraw from the EU.

Also, while a nation can withdraw, the EU treaties make no provision for the expulsion of a member nation.

(http://en.wikipedia.org/wiki/Withdrawal_from_the_European_Union - since I'm not on my own machine right now I can't quote using Tribext.)

A Grexit ain't gonna happen. At least not within a timeframe that has any immediate relevance.

The fact is that what we're experiencing right now is a top-down disaster. -Paul Krugman