"Is it enough? Is this any different (or any more successful) than the business cases we’ve been making for intranets?"
I’ll start with answering the first question, if the business case is enough. Well, obviously it is not be enough for any purpose or audience. But hopefully it says enough for the purpose of getting someone in management interested in listening to what kind of value that E2.0 can bring to their business. For someone in management who is not really aware of the potentials of E2.0 but rather sees it as a hyped buzzword, then two minutes is just about what you can get of their attention to make the case. They certainly won't read a book or even an article that expands on the business case.
Regarding the second question I would say that it is more or less the same business case as has been made for intranets. What is different is that it will be more successful.
Traditional intranets have certainly helped to improve (primarily one-way) communication and access to (a rather limited set of centrally selected) information assets. But we all know that there is a lot of room for improvement and that we need both new solutions and new ways to improve real-time communication, content-centric collaboration and many-to-many conversations. Intranets are not very successful in any of these areas. An intranet site or portal is primarily a communication tool for the organization, not for the coworkers. It is only natural to look around for new solutions to (almost) the communication and collaboration problems that enterprises face (Enterprise 2.0).
It is important to understand that previous solutions to the problem of communication and collaboration - such as intranets - have not really addressed the social dimension of communication and collaboration. They have neglected how important it is to motivate people, to encourage and reward them for contributing, and to help establish the trust an informality that is needed for people to communicate and collaborate with each other. Traditional intranets have not really been very successful in motivating people to communicate with each other. They have not trusted coworkers enough to let anyone get access to information and contribute with their own, or to have free-form conversations about just about anything. Intranets are still perceived as tools designed, controlled and used by the management to provide them with information that has been approved by the management. If intranets would have been designed for people, as places where coworkers are free to communicate and share information with each other, then the whole Enterprise 2.0 thing would not be such a big deal.