I have to say the BBC coverage is a bit one sided, watching it you'd think that the whole summit was about Obama. They barely mention the other leaders.
http://search.twitter.com/search?q=%23g20+OR+G20
That Twitter stream will give you a better overall view than the BBC will.
On Radio 4, it seems to be all about Gordon Brown! Obama only received a passing mention; even Sarkozy got more coverage.