Well now we have the official answer.
"I don't think it's a matter of a one-night stand. I think we now go into the next day's breakfast" said the president in answer to my question about how we would feel on the morning after the heady night before. And, what's more, Gordon Brown agreed.
In fact, Nicolas and Gordon - this was an all "first name terms" affair - agreed on pretty much everything when and if they could.
There were mere hints of disagreements still there on agriculture, the EU budget and NATO. Even on the one topic where they did split - whether to boycott the Olympic games ceremony in Beijing in protest at China's crackdown in Tibet - the two men were careful to explain why they disagreed. Brown, Sarkozy said, was the host of the next games whilst he would be in the EU president's chair and would have to consult the other members.
I spoke to Arsenal's manager, Arsene Wenger, after the summit at the Emirates stadium. He'd been invited to join the leaders for lunch and was struck by how well they worked together and at how Britain no longer looked exclusively across the Atlantic and France no longer across the border to Germany for friends.
This then did represent a concerted effort on both sides to put the bitter rows about Iraq, "our money" and their farmers behind us.
Let's though see how we all feel at breakfast time or - at least - the next time there's something real that divides the two nations.
Emirates stadium, Arsenal, North London
We've been flattered. We've been charmed. We've been wooed. And I'm only talking about the French president and not his photogenic wife, Carla.
Nicolas Sarkozy's mission on this trip has been to seduce the British public as he did the French electorate and, of course, Carla too (but more than enough has been written about her already). This, I confess, leaves me feeling rather like the prime minister did last night at Windsor Castle - aware of where I am and yet somehow feeling lost.* At every Anglo-French summit presser I've attended my job's been simplicity itself - simply light the blue touch paper and watch the differences explode in a mixture of Gallic indignation and British exasperation. So, now what are we to do?
Sarko's words of praise for Britain - not just for our role in two world wars, not just as the founders of parliamentary democracy but also as a model since - go way beyond what any previous president has said. Sarkozy and Brown have a shared history of waiting impatiently for the top job, of soaring and then plummeting in public esteem and of genuine mutual admiration. Today they are announcing co-operation on immigration, the economy, defence, development and nuclear power to illustrate the rhetoric about a new Franco-British fraternity". And yet and yet...
Britain has always seen France's concept of European defence co-operation as a potential threat to NATO and not something that underpins it.
Britain continues to promote free trade whilst France under President Sarkozy continues to talk about protectionism.
Britain wants radical reform of the CAP and European budget whilst France will fight to protect her interests.
Now, you may say, countries will always have differences and they will always pursue their national interests. What matters is the mood with which they approach the problems that emerge. Certainly, this visit feels very very different from the icy Chirac/Blair summits - at least the ones in later years.
However, the question hanging over this "entente amicale" is how will we feel the morning after the heady night before?
* Hats off to my colleagues at ITN who noticed the Queen waiting for Mr Brown to arrive at last night's Windsor banquet and remarking that "Well the prime minister got lost. He disappeared the wrong way…at the crucial moment".
