If you're traveling from the United States, Canada, and several other nations, your trip to Greece just got considerably cheaper as the Euro drops in value on fears that the Irish financial crisis may spread. Previously, the Euro had risen sharply over the last month or so, in part over uncertainty about the U.S. midterm elections and the ongoing financial fears in the U.S. itself.
Some people get fanatical about getting the very best exchange rates and timing their major purchases in Greece to days when the the exchange rate is at its best... but on a daily basis, the difference is usually slight and likely to be consumed by various banking and exchange fees anyway. Usually, it's not worth worrying about, but if the exchange rate happens to be improving during your journey, it's a nice bonus.
On the other hand, in bargaining on major purchases, I've occasionally been able to shave a little extra off the asking price by pointing out that I'm suffering from a terrible exchange rate at that moment and really shouldn't be making the purchase at all...
Tips and Tricks on Using ATMs in Greece
For a more technical look at the Euro financial crisis right now, including some of the reasons and problems behind it, Sean O'Grady's article from the The Independent is worth reading: Desperate fight to save the euro.