I am skeptical, to put it mildly. One reason the G-7 (before Russia was a member) made sense is because the member countries not only are economically important, but also share fundamental beliefs in market economics, representative democracy, and the rule of law. it never was simply a matter of GDP rank.

It was strange enough to give Russia a seat at that table -- but that was done in the heady early days of post-Communism when optimism abounded. But the idea that Argentina -- which for nearly a century has been the poster child for how government can turn a resource-rich nation into an economic joke simply by being deliberately stupid -- should help guide the world economy is disturbingly ludicrous.

Of course, for that very reason, the change may prove to be illusory. An overinclusive G-20 could easily end up like so many of the UN's comic organs: a place where substantive agreements are exceedingly rare, and a forum for countries that wouldn't know the rule of law if it hit them in the face to harangue the evil West. If the G-20 does degenerate into such (rather expensive) uselessness, then real policy will end up being made by an informal subcommittee of (gasp) 7 or 8 or so. Creating another grand but useless international body, while making real decision-making less transparent, does not strike me as progress.

For the record, here are the groups, according to Wikipedia:
G-8
Canada
France
Germany
Italy
Japan
Russia
United Kingdom
United States
European Union

G-20
Argentina
Australia
Brazil
Canada
China
France
Germany
India
Indonesia
Italy
Japan
Mexico
Russia
Saudi Arabia
South Africa
South Korea
Turkey
United Kingdom
United States
European Union

While I could make the argument for some of those countries... yes, the G-20 expansion is (at least in my mind) just a way to blow wind up the skirt of some of these countries. Adding Saudi and Turkey is a way to add a carrott to countries like Iraq and Iran.

Yes, we need economic advice, consent and counsel from Indonesia??

That's like Wal-Mart asking seeking a summit with Bob's 5 and dime.