Doc Searls has extended the thread on RSS and e-mail, and approaches the discussion from a relationships perspective. As technology people, too often we focus on protocols and the implementation details of software and not enough on what people are trying to accomplish. Is RSS as we know it a good replacement for e-mail? Certainly not. But from a functional perspective, there is some overlap in what RSS can do and what you can accomplish through e-mail. Since RSS can support authentication using HTTP and is an opt-in technology, there are certainly scenarios where it makes sense to use it over e-mail.
Many users are viewing RSS like a telephone that only makes outbound calls and has no number for incoming calls. They don't have to worry about people that they don't know getting their phone number and bothering them, but they can pick up the phone and can connect with anyone they want to when they have the time to do so.
UPDATE- Based on a comment, let me clarify. I'm referring to users that are leveraging RSS to read content, not publish. Today, if you subscribe to mailing lists or other content sources with your e-mail address, you can end up receiving content that you never wanted without your permission. With RSS, you have to request what you want and you can easily unsubscribe at any time.