Let us address the question first from a parochial perspective. Was the Prime Ministerial energy worth it for the Prime Minister? For months the G20 summit was seen as one of the few levers available to Gordon Brown in the build up to the next election. Will it help to boost his ratings in the opinion polls? The answer I suspect is a complex one. I would be surprised if the summit gives Brown an immediate lift in the polls. Voters are too worried about their own jobs and the grim state of the British economy to offer their gratitude for an event that inevitably seemed far removed from their lives.
The gathering was literally removed with glamorous leaders cocooned in a security bubble. The focus of the leaders' attention was also not immediately accessible for voters who have lost their jobs or are worried about such a prospect, with the talk of trillions and billions, loan guarantees and detailed regulation. The communique reads like the British government's comprehensive spending reviews, the figures are large and the means by which the cash will benefit voters not obvious.
But the summit will deservedly give Brown more self-confidence as a Prime Minister, one that can command an international stage. He got a fleeting confidence boost last autumn when Nobel Prize-winning economists credited him for supposedly saving the world, but he has never recovered fully from the non-election fiasco in the autumn of 2007, a still underestimated calamity. After the last few days Brown would not be human if he did not get a buzz from the glowing words of support from President Obama.
The summit was very much his personal project, pioneered amidst jeers from parts of the media which predicted gleefully at one point that Obama might not even turn up and the disapproval of some Blairite Labour MPs, for Brown the familiar debilitating coalition.
Displaying the usual intimidating resilience he carried on working around the clock to make sure the event worked at least as an act of stunning political choreography. He pulled it off. Confidence is an important part of a leader's repertoire. When Brown acquires self-confidence he tends to be a more formidable operator. We shall see.
What of the substance of the communique? Quite a lot of the exchanges at Brown's press conference yesterday afternoon were not especially accessible but he gave one answer which had a ring of truth to it: "If you've got a global crisis you've got to get the leaders together to act. That's what I have been trying to do".
Brown views the economic crisis as a global one that can only be resolved by an internationally co-ordinated response. His army of opponents argues that this is a convenient interpretation as it absolves him of direct responsibility. But even his harshest critic must accept that this economic crisis is not afflicting Britain alone. The notion that somehow or other by coincidence the rest of the world also has a few difficulties has always been comically far fetched.
If it is accepted - as it surely must be - that at least Brown has a point about the global context, the G20 has made some significant reforms. Without the focus of yesterday's gathering they would not have happened so extensively or speedily. The changes and the additional sums of cash might not prove to be extensive or speedy enough, but they are incomparably better than a vacuum in which leaders act separately.
The fact that the gathering loomed was in itself a discipline on leaders with the private negotiations of recent weeks inevitably the most productive part of the entire sequence. I spoke to one of those at the heart of the British negotiations several days ago and he told me then that the focus then was on the IMF. He was optimistic about the additional funds that would be made available to it. Yesterday the optimism was realised.
Arguably more important they all agreed on a financial regulation package in which the crackdown on tax havens is the most vividly accessible ingredient. As a whole the package extends well beyond tax havens. The global era of the light touch regulator was doomed, but it came to a formalised end in London yesterday.
The limits of the summit are easy to highlight and are important. Even if the leaders had agreed on every item on Brown's original agenda they would not have been in a position to compel the banks to start lending again, or rather they have chosen not to be in such a position. Until the banks start lending the crisis will continue.
As has been written up gleefully many times by Brown's opponents there will be no new collective fiscal stimulus, although this was always an overblown aspiration. As one of Brown's allies now points out to me "We would never have accepted a demand from say Germany or France to spend more money in the UK against our wishes". Currently Germany and France are resistant, but they might change their minds before very long. The attitude of different leaders towards a fiscal stimulus is more fluid than they seemed to be at this summit.
After the energy draining high of recent days Brown will return to humdrum realities, the prospect of a budget later this month with no spare cash to spend, MPs' expenses, the row over what his City Minister Lord Myners knew about Sir Fred Goodwin's pension.
Probably the slightly better economic news yesterday, with indications that the housing market is showing signs of life, is more significant than yesterday's summit in terms of the government's immediate electoral prospects – and there will have to be many more such signals if the Government is going to narrow the Conservatives' lead in the polls.
But given that leaders spend much of their time in Downing Street pulling levers which have nothing at the end of them (ask Blair) the last few breathless weeks were an example of Prime Ministerial time spent constructively. As a result Brown's authority is enhanced.