I recently went to one in Boulder (and full disclosure, I work for a sponsor, but I participated like any other non-sponsor there) and I thought it was a great time. You're probably not going to launch an actual startup by Sunday. You will meet interesting and smart people. It's also good practice for hashing out ideas, setting priorities, honing a pitch, presenting and doing other startup-y things in front of real people. And if you're a developer you have an excuse to try new things out with framework or language you've been wanting to try using.