Twitter.com is not a protocol, it is a service. I think it is also important to note that it isn't a public utility either. right now it is dangerous to place all your eggs in a single basket. When you only have one service provider you lose control of things such as dependability, namespace, access, etc. These are things that most may be willing to let someone else provide for them, but some may want to control these and other aspects of microblogging. A federated design with multiple independent service providers would go a long way to help fix these shortcomings.