App.net tried to do this, and failed miserably. The Twitter "firehose" (all public tweets, delivered in real-time) is likely very valuable for news, research,

App.net tried to do this, and failed miserably. The Twitter "firehose" (all public tweets, delivered in real-time) is likely very valuable for news, research, and marketing interests; charging for access to the firehose is possibly a workable business model, and by limiting it to public tweets, side-steps many of the issues around privacy and user tracking (since the people writing the tweets are doing so with informed consent, even if individual tweets may be sent in error).