I haven't been able to think the whole concept of "stamps" for email. Seth Godin has a pretty good argument for them (Seth's Blog: More on stamps). I'm starting to agree that it is a good idea, but as a marketer at a small business I do start to worry about the overall costs. For our average customers, we probably communicate via email at least 7 times:
2. Purchase Receipt
3. Free webinar training announcement
4-6. Additional offers for opt-in customers
7. a technical support incident
So, we're only talking $.07/user. That's probably worth it for a good customer experience.
But Seth brings up another concept: RSS feeds. Here's an opening for an entrepreneur. Right now, RSS is one-to-many communication. In order for RSS to work as one-to-one communication is has to be secured with encrypted URLs that can be only read by the intended recipient.
Once RSS has that, it will be a viable option. Until then, I think we'll have to pay for email stamps.