G20 hit as Greek PM threatens to quit

Try attending a meeting with Greek colleagues fighting under the table, exchanging black eyes over the fate of their country and currency, alongside a collection of Italians screaming about their own debts and economic reforms (or lack of them). Imagination isn't needed: the G20 summit will be a touch testy today. What's it about, and what is it likely to achieve - beyond the usual platitudes - if anything?