The first thing is to actually talk to your potential users. I don't think bloggers are going to be of much help in this phase. You are looking for feedback and want to talk with real users.

I would not spend time creating a screen cast yet. If you have a few screen shots or can just describe the product to them directly. Ideally you would want 10 passionate customers. If you only have 1 or 2, their feedback might drive you in the wrong direction.

As technical people, we would love to just email a few people or post a comment on a blog. But to get great users, you have to engage them. The best way is to go out and physically talk with them. Since your market is restaurant/cafe/bars, you can do it all locally which is great because you can read their body language, watch them use it, etc.