RSS is a big buzz word right now, and this question has been popping up all over place.
Will RSS ever replace email?
In short, answer is no.
RSS will never totally replace email because they each do totally different things.
RSS was designed for a totally different purpose than email, and technologically speaking, it would be impossible for RSS to do everything email can.
Consider this analogy: RSS and Email are like TV and telephone.
If you want to reach a broad audience of spectators, you use TV or RSS. Consumers like TV because they hold remote and can change channel at will. They have total control. Likewise they can an RSS feed at any time if they so choose, and instantly source of information is totally gone, never to return against person's will.
Email is like telephone: You can email or call anyone based on their phone number or email address, and they can call you or email you back. Consumers like email and telephone because of two-way communication. But with two-way communication comes possiblity of having annoying telemarketers and spammers along with it. And boy do they come!