I agree. To me, they need to be able to see it.

If they want to listen to the radio or watch tv, post a pic to the gallery, play the arcade...anything like that, they have to register. Otherwise totally open.

3% to 5% signup ratio is what you can expect. like the guy above said, if your really kicking ass you can maybe double that. but you should be happy with 3%, that 3% can really add up if your audience is large enough.