MTV is Reporting that MS will roll out a Public Beta of the service in Mid Late oct and will be be out with a ad Campaign it looks like by "black friday"
http://kotaku.com/5375612/xbox-360-dash-update-for-twitter-facebook-lastfm-enters-beta-soon
http://kotaku.com/5375612/xbox-360-dash-update-for-twitter-facebook-lastfm-enters-beta-soon