I like OpenFeint too, but there are some things to keep in mind. First, integrating OpenFeint adds a few MB to your app size if you support both landscape and portrait modes (I'm not sure what the exact size is - sorry). This can be an important consideration if you're close to the over-the-air limit. Second, Free Game of the Day is a great program, but it is something you need to apply to. Not every game gets accepted.