Ironic that this thread started a mere hour after I had left a (very!) late night at work (in this timezone), more or less in order that I avoid the whole business. And get a lot of extra work done. (Which I'm not sure I did, but I got some done, in-between procrasti... Ooh shiny!)
Nothing against the kids doing anything (earlier in the evening, when I went out from work, temporarily, for some food) I saw some kids doing their thing, and some older lads either doing-what-they-normally-do or possibly going to do a no-costume version of trick-or-treat[1]. But in past years I've spent the evening in the house with the lights off listening to the radio, just to save the trouble of getting to the end of anything I'd bought[2] or saying "Whoops, forgot, sorry!" to anyone on my doorstep.
One year I went to a party. As a ninja. I'm sure there's something Freudian/Jungian about that, given I tend not to go to parties much and, when I do, generally stay in the metaphorical (or even actual) shadows. Still, it got me out of the house.
Anyway, from the younger ones (the ones with accompanying parents, who often get into the spirit of things) at least try. Beyond that (and actual themed parties/occasions, which you'd not really notice unless it were one of your neighbours' houses) it's perhaps a bit more like an annual Begging Sugary Things Day.
The same sort of age-dependant attention to detail also applies to the occasion Guy Fawkes one might find being exhibited in some convenient High Street doorway or shop frontage (location being dependant on the respective shop-staff's knowledge and/or permission). I've seen brilliant ones, and some that were only obviously a Guy ('bundle of rags' being an overstatement) because there were requests for monetary donation. I suppose that, these days, it's almost inevitable that all but the most impromptu creations are probably going to bear a V For Vendetta mask, but I've not seen any yet, at all, this year.
[1] No threats, but no effort. Like sometimes you get with impromptu carol 'singers' who have the one song, and no more than a couple of verses of that.
[2] As I use to the years immediately following the first year in this house. The very first year, I think I broke out a fresh pack of Pringles and some packets of mints, whatever else I could raid.