Signed up for one next month mostly because a friend guilt-tripped me into it. Part of me thinks it's a weekend I could put into the project I keep not finishing. Did a hackathon ever actually do something for you, a job, a teammate you kept, a thing you could talk about for twenty minutes in an interview? Or is the honest answer that it's fun and that's the whole return?
Mine got me a teammate, not a job. We still build things together four years later and two of the roles I've had came through him. The demo itself is completely dead, nobody has opened it since Sunday afternoon.
So, go, but go for the people in the room rather than the thing you ship.
Opposite experience here — mine was a disorganised mess, half the team had vanished by hour ten and I came away with nothing but a wrecked back. The thing I'd check now is the theme: sponsored ones with a real problem attached were worth it, the generic "build anything" ones were chaos. Look at who's judging and why they're paying for it.
Two people I met at one are still the people I send code to, so mine paid off sideways rather than on the CV. The demo itself has never once come up in an interview. If you go, go for the people and join a team you don't already know — chase the prize and you'll spend 36 hours building something you can't maintain and will never open again.
