I agree. Properly organized hackathons (that aren't merely a front for recruiting people) are great fun if you like the vibe of working around other people with a major time constraint. It forces you to come up with some clever ideas.
That said, I tend to work on my own or in a pair at these events. It's great being around people but ensuring you get reasonable consensus in a larger team is hard work and ideally demands you know your team in advance.
P.S. I think tickets might all be gone now, but http://leedshack.com/ is next weekend. British readers might want to keep it on their radar for future reference as the last one was awesome.