I think you're being too optimistic about the number of non technical people that will use this service. For them to do so would require them to understand what blogging is, why they would want to keep a blog and how simply mailing your posts is an improvement over typing something into a web form. Posterous is a fantastic idea (IMO anyway) but I doubt this will happen anytime soon.

I'm guessing your audience will be tech savvy users who understand why publishing some conversations online using a tool you're already using anyway (email) is a good idea.

Not that there's anything wrong with that, of course.