The North American tour is over for another year, and as ever one is struck by the difference - in every conceivable respect - between the two events, between Montreal and Indianapolis.
In terms of local enthusiasm, there is no comparison. In Canada they are nuts about 'open-wheel racing' in general, and about Formula 1 in particular: it's a given that the Circuit Gilles Villeneuve will be sold out on Sunday, and close to it on the practice and qualifying days, too.
This year it had been thought that the absence of Michael Schumacher and, overwhelmingly, Jacques Villeneuve, might have an adverse effect on the gate, but not a bit of it.
The track itself is pretty good, too, and remarkably unforgiving by the standards of today. Given that it is hemmed in by barriers, a mistake here means a bent car, rather than a couple of seconds lost. That being so, the Canadian Grand Prix traditionally features more retirements than usual, and a busy afternoon for the safety car.
As a circuit, it is considerably more testing than the F1 layout at Indianapolis, where the blast through the oval section is exhilarating, but the infield section way too tight. What makes this race special is not the track, but where the track is. If you can drive through the gates at the Indianapolis Motor Speedway and feel nothing there is something wrong with you.
That said, I speak as one who grew up besotted with the Indy 500 and all its legends, and for anyone not touched by that going to the IMS will of course be a more mundane experience. Every year I get out of Montreal at the earliest opportunity and head for Indianapolis, but there are those who leave it to the last second.
Once you've arrived in Indy, you're aware of a very different atmosphere from the one you recently left. For one thing, as a journalist, you have swapped incontrovertibly the worst press facilities in F1 for consummately the best; for another, you are suddenly in a place where the world does not revolve around grand prix racing.
In Indianapolis, racing is in the air you breathe - but it doesn't quite extend to F1. In the case of so many people you encounter, you have the impression that fundamentally they want to understand F1, even to love it as much as the rest of the world, but somehow they just can't quite get it.
As I mentioned in a column a year ago, a lady in my hotel asked me - very politely, even apologetically - if overtaking were actually allowed in F1. She wasn't being facetious or - Heaven Forbid! - ironic; she had simply formed the impression, from what she had seen on TV, that processions were what F1 was all about, and that to even mention racing was perhaps a little bit parochial, even vulgar.
I assured her that, no, she hadn't got it wrong: there was way too little passing in F1, and I could understand how this was difficult to comprehend for anyone imbued in oval track racing.
Several times - prior to the CART/IRL split - I was in Indianapolis for the 500, and invariably felt that, for a few days, I was at the centre of the universe. Wherever you went, nothing else was being talked about, and the Indianapolis Star devoted pages and pages to it.
When you're there in grand prix week, however, it's a little different. It wasn't until the Wednesday that there was any real mention of F1 in the paper, and although Lewis Hamilton had attracted headlines across the rest of the world, the only racing story of consequence in the US, it seemed, was that Dale Earnhardt Jr was switching teams, and - as of the beginning of the next year - will drive for Hendrick in the Nextel Cup series.
Seemed to me a touch sad that, in Indianapolis of all places, there should be this confirmation of NASCAR's stranglehold on motor racing in America, and I felt the same when I visited the track's glorious museum - and, upon entering, was immediately confronted with a stock car...
Still, that's the way it is. For a variety of reasons too disparate and involved to go into here, 'Indycar racing' chose to shoot itself in the foot, and the NASCAR juggernaut continues to crush all before it.
That being so, it's hardly surprising that F1 - not even an American form of motorsport - struggles to get a foothold that side of the pond, and its case is hardly enhanced by local journalists like Star columnist Bob Kravitz, who joyfully pour invective on it.
"The worse F-1 (sic) treats everybody," wrote Kravitz, "the more disrespectful they become, and the more IMS and the city beg for their love and attention.
"And it's got to end the moment today's glorified, hi-tech parade lap through and around the Speedway is finished."
The basis, of course, of Kravitz's ire lay in comments by Bernie Ecclestone, to the effect that F1 does not need America. A little research would have told him that Bernie says much the same on an annual basis about other countries, like... Britain.
It's a common trait across the world, it seems to me, that folk feel free to criticise their own countries - but God Help you if you presume to do it for them. Americans are not exempt from this rule, and Kravitz clearly feels patronised by what he describes as, "Arrogant F1" - sorry, F-1.
That's his right, and I have no quarrel with it. What did make me angry, though, was that later in his piece he wrote this: "In 2005 F-1 pulled off a stunt that should have earned them eternal banishment from IMS.
"That was the year of the Great Michelin Exodus, and while F-1 tried to make good with the people who got stood up there, they still ripped off thousands of visitors who had spent their hard-earned dollars to come in from other states and countries. It's a pattern of abuse and arrogance, and Indianapolis should no longer let itself be bought off by these clowns."
Proper cross, Mr Kravitz, as you can see, as was a bloke I encountered - a huge racing fan - who said, "Went to the grand prix every year until '05, and after that said I'd never go back..."
I'm the first to admit that, for grand prix racing, that was a shameful weekend. Michelin simply got it wrong, but at least were honest enough to admit it, and to make some financial reparation to fans whose trip to Indy had been ruined. Attempts to find a way round the problem were hardly aided by the powers-that-be, and the whole event turned into a fiasco which made F1 look ridiculous.
No argument there. The point, though, that Mr Kravitz and others seem to have missed is that Michelin were not in a position to guarantee the safety of their tyres on that track; had everyone taken a chance, and had there been an accident perhaps involving members of the public, can you imagine the consequences in America, the most litigious society on earth? Can you imagine, for that matter, what some columnists might have written?
Years ago a friend of mine went to the Indy 500, thereby fulfilling a lifetime's dream. It rained. Back to England he flew, having never seen a car at the Brickyard. I don't seem to recall his saying it was ridiculous that Indycars didn't run in the wet. S*** happens, as they say.
In spite of Mr Kravitz, and people like him, my feeling is that a great many folk want the US Grand Prix in Indianapolis to survive and thrive, which is why I hope Ecclestone and Tony George can reach agreement on a new contract. This weekend we're off to Magny-Cours for what could be the last French Grand Prix for a very long time. Don't let's lose America at the same time.
Incidentally, the day after the US Grand Prix, Mr Kravitz wrote a rave piece about Lewis Hamilton, comparing him with the young Tiger Woods. So maybe F1 isn't so bad, after all.