They are an international phenomenon. I see them, along with startup culture, happening in pretty much every Europe centre too.
Turns out its a video game. Respectable enough hacker hobby.
My only regret has been that I've been too darn busy to host another!
Jon is spot on when it comes to our community. There has been a pretty big spike in Hackathons around here. I have noticed a lot more talk about it on the internet as well.
For somebody unfamiliar, where does one go on the Internet to find the beSt list of similar events near by?