I don't know man. It would be nice to be able to go to Europe and not have to pay retarded amounts of money because the Euro is stronger than the Dollar right now, BUT...
An example of why global currency might be a bad idea: Greece. Now that all of Europe has one currency, Greece's economy collapsed... and it might drag everything down around it just because they have the same currency now.
buisnessweek
Practically unnoticed by the public, an issue has returned to the forefront in recent weeks— the fear of a national bankruptcy in the euro zone. And the question as to whether such a bankruptcy, should it come about, could destroy the common European currency.
Greece was always at the very top of the list of countries at risk. But now the danger appears to be more acute than ever.
http://www.businessweek.com/globalbiz/content/dec2009/gb2009128_445076.htmFrankly, I don't know a lot about currency or exactly how all the details work, what with trading and stuff, so I can't really say. In theory, a lot of things sound nice. In theory, this does too. I just don't know enough about the idea yet.