Has anyone attended a monthly "Hackathon"?

I'm ramping up my startup more and more and as a sole founder, I would like to network (I use that term loosely, it's more hang out) with other people in a similar situation. I've seen a few meetups in the Philly area for hackathons where it's billed as people coming together to hack on their startups...which sounds exactly like what I was looking to do.

Can anyone speak from experience what to expect at these things? I'll most likely attend next months meetup and would like to get an idea before I head on over. Thanks.