alt Hacker NewsPractically all corporate backed or organized ones are more or less lots of job interview tasks running in parallel, so they get lots of work for free on a problem they really should've paid people to solve, and get to pick the result they like most. I've always found the idea too exploitative to ever join.
I went to a London one once and this was totally my impression of it. The free beer and food was a drop in the bucket for what the massive corporate got out of it at the end.