What can the G20 achieve?

The G20 summit commences in London this week fittingly surrounded by the trappings of the failed industry of London's Docklands.
One of the main debating points of interest will be the response to the call for increased and continued 'stimulus packages' which are threatening to eat away at the future economy. The second major issue will be discussions about regulation and control of the financial elements that have led us into this crisis. Can the 20 world leaders turn the world around in 24 hours? - one has to have serious doubts whether they will achieve anything beyond making the right noises before going back home to create measures to protect their own economies - and of course market protection will be on the agenda for the world leaders to pay lip service to.
China has major concerns about the devaluation of the dollar particularly as it holds so many dollar assets, and it is rumored that they will attempt to table proposals for a world currency for greater global economic stability. There is not much serious hope of this motion gathering many subscribers.
I should point out that although widely referred to as the G20, it should probably carry the title G22 since Spain and The Netherlands have been additionally invited to attend. Other organisations such as the IMF are also expected to be represented.