As a hackerspace guy, I’m sort of ashamed to say I’ve only attended one (hardware) hackathon, a ‘build stuff out of junk in our boneyard’ (as the feedback you got indicated, themes are very important) event at Louisville’s amazing LVL1. Depending what angle I look at it, it was awesome (meeting the LVL1 folks, talking to people in other teams and seeing what they were doing) or a total disaster (our team never really gelled and by the end everybody had gone off and done their own thing — I really wanted to leave before the presentation part happened). So I didn’t exactly rush to recruit a team for the next one.
I did have a better experience when we hosted ‘Build Nights’ which was something Instructables did for a while. They sent us stuff, we got the word out about the event, then they asked us to generate at least 2 Instructables from the event. So these met the important criteria of having a somewhat defined domain (no IoT vs. iPhone game scenario) and fairly clear (though not that restrictive, really) goals. I also did these as 3-hour sessions on two evenings, so there was no giving up of weekends required (you’d just likely feel tired and crappy at work the next day). Overall that worked well from my perspective, but I think they’ve discontinued that program for now. Maybe a bunch of deadbeats grabbed the free stuff and were never heard from again.
I liked the idea of doing more of a ‘book club’ type of thing. Similarly I’ve pondered doing local study groups for MOOCs (with other people following your progress, you’d probably feel a bit more motivated to power through).
In general I’d file hackathons under ‘I love the idea but the reality is not so great’. It’s really hard to get the right balance of social mingling and getting real things done.