Prediction: MySpace fails within two years - users move to something similar, but less restrictive. I'm not sure trying to create that something is a good bet for a startup though; there seems to be more random chance involved in determining the success of such a service than anything. That's not to say it's impossible. To anyone thinking of building a similar service: make it flexible, easy to use and free of arbitrary restrictions. Pay special attention to the social interface (see http://www.joelonsoftware.com/articles/NotJustUsability.html).