In no particular order ...
It's odd using paper money, especially when each denomination is pretty much the same size and colour. It's even odder using $1 bills.
Toilet bowls fill very high. It's the same in Canada. Much higher than in Australia. I assume there is less need to conserve water?
Prescription medications are advertised on TV all the time. That in itself seems odd, but what I found most amusing was that, invariably, most of the ads' running times are taken up listing all the side effects or "don't take if you..." disclaimers.
There was a constant buzz of black helicopters taking off and circling Washington DC. Felt a little unsettling.
The realisation that I have an accent and that I have to sometimes make an extra effort to speak more clearly for Americans. The other day I had trouble just asking for postcards.
I knew there would be lots of yellow taxis in NYC, but I didn't realise how many. Each time I stopped to take note I would say at least half of the traffic would be taxis.
The street and avenue numbers in Manhattan make it so easy to work out where you are and how to get somewhere. For a city this large it would be painful to have conventional street names.
There was a preview for DocNYC, a documentary festival, prior to the French film I saw. So many documentaries! I think the program said over 100. Looked really great too.
Generally, I felt quite safe walking around Manhattan. No more unsafe than any other city I've visited. Mind you, I was always careful to be conscious of my surroundings. There were a couple of times I stumbled into areas where I felt a little uncomfortable but quickly regained my bearings and was fine.
My regard for American people in general has greatly increased. The trip has blown a few stereotypes and I've found people to be generally very courteous and polite. The rude ones have generally been the tourists!
If you're a walker like me you can get a long way around Manhattan on foot plus a few subway trips.
I came across a chocolate store that had "potato chips covered in cheese flavoured white chocolate". I kid you not.
In the day or two following the New York Marathon I've seen many people wandering around with their participation medals on proud display.
And these last two aren't anything to do with the US but I just remembered them ...
I met a chap on The Canadian train who is a business analyst for an energy company who are also implementing SAP, just like Origin. It was interesting comparing notes.
There was an interesting line in the French film that basically said it's wrong to describe animals (other than humans) as naked, because the word "naked" suggests or implies you are without something. I'd never thought of the word like that.