This is very cool.

Since you're asking for feedback, here's mine: Definitely add GPS as an option.

Maybe you can hook into Google Places or Foursquare to find the location or address. You can narrow it down to individual stalls if you want to give the user the option.

I know there are a lot of good reasons not to use GPS here, but it seems like having it as an option would definitely help so that people can get involved by just using the app.