looking forward to applying some of this at my first hackathon. do you usually come in with an idea, or wait until after getting there to think of something?
It's totally up to you. Some hackathons are themed, so a lot of times you'll want to hear presentations from various API sponsors first and then decide how to integrate. Conversely, in the case of http://ramen.is, we had planned out the idea for quite a while before going into the LAUNCH hackathon last November.
I've done both, sometimes when I get there and see an API from a sponsor that I had missed before, it'll give me a great idea on the spot. Other times with VUE I'd been planning the idea in my head for a couple months.