It might be out in 2009, but that's really pushing it. I hear that it maybe be a Second Edition to Vista or something like that. It won't be a major OS, but more like an update.
Like what? I know it has compatability problems with older video cards, but that's mostly the problem of ATI and nVIDIA as they make the drivers. Microsoft doesn't.
Depends what you use it for. Home Premium is great for most users since it has good media and gaming capabilities. Business runs games just fine, but don't expect anything special in the way of media. No Media Center for the Business Edition.