People see the conversation, and that is valuable. Public customer support is how Twitter is going to make money (in part). IM clients are extremely distracting

People see the conversation, and that is valuable. Public customer support is how Twitter is going to make money (in part). IM clients are extremely distracting. Real-time but asynchronous messaging is not the same as synchronous messaging. You can block people on twitter, and log messages. Better than that, you can access the conversations via an API.