I'm from rural Ontario and Jack and Jills are super common, DH is from a major city and until we started dating, he'd never been to one.
How they work where I'm from:
* They are generally held a month or two before the wedding.
* Word of mouth (in a community of 500, not hard) also the community centre has a bulletin board that advertises upcoming events.
* Tickets are about $10 or $15 per couple this gains entrance to the event, some food (usually finger food & cake), soft drinks, and a dance. Alcohol is usually sold much cheaper than a bar, but high enough that the B&G still profit. There are also games (about $1 a play) and raffles.
* Anyone in the community is welcome. Generally people take these as a chance to have a night out, as well as wish the B&G well. From experience there's a pretty wide age group, pretty much 19 (drinking age) to about 60. I have been to many J&Js where I haven't been invited to the wedding, but just wanted a fun night out or to wish a couple I liked well.
* The event is organized by the bridal party, who generally contribute prizes and so on. The B&G receive the profits, after the costs have been covered. Where I'm from it's not normal to get donations from the community.
As I said, to me, their the norm, but DH had a hard idea with the concept and still finds it weird. My explanation is that it's not so much a cash grab, as a community thing. It's seen as a nice night out, but also a way to wish a couple well, even if you may not be close enough to go the wedding (example, you went to school together or your friends with their parents). I'm not sure they would work outside the rural setting, without that sense of community (where I'm from, most people have been there for generations, your grandparents went to school together).