We were lucky enough to be in the US for Hallowe'en last year, something that was a completely new experience for me. In particular, I wanted to see how trick or treat is done properly, since in the UK we know it as an American tradition.
Of course, as we were staying in a hotel, no costumed kids were going to come to our door - so we had to make an effort to get out there ourselves. After taking a bit of advice from friends who live locally, we headed to the small town of Ellicott City for their Trick or Treat evening. The night had a festival atmosphere, with almost every shop on Main Street participating by handing out goodies to all comers. (Even un-costumed, slightly-bemused Brits were offered plenty of candy!) The fact that all the stores were involved (most often with the staff in costume, too) made for a really nice atmosphere.
I loved that everyone, from the littlest kids to fully grown-adults, was getting into the spirit of things. There were whole families decked out in matching outfits, and even some dogs were getting in on the dressing-up action. Insofar as I've seen trick-or-treating done in the UK at all (which hasn't been much), I've only ever thought of it as a kids' thing, but I'd guess about half of the adults were also dressed up.
The variety of the costumes was great, too. I tend to think of Hallowe'en costume options as consisting of witches, vampires, and zombies... but while there were a few friendly witches around, the Ellicott City crowd overall was far more diverse. While many of the costumes were obviously bought off-the-shelf, there was also a lot of innovation going on, with some of the most endearing costumes made from cardboard boxes and tissue paper.