I recently came across a great article on the future of deliverability.
Quick overview: We all know that when a subscriber clicks the \”report as spam\” button, the ISP gets data to help them make decisions about what they want to do with a senders email such as block or send to the spam folder.
ISPs fight spam in a bunch of different ways, reputation, authentication, content blocking etc. 
This article talks about how ISPs are starting to use other types of data such as, \”subscribers who do not open emails\”, to punish senders with poor best practices. Its all coming down to a marketers reputation.
If email marketing is important to your company and drives revenue, I suggest you work with an ESP (Email Service Provider) who can stay on top of changes like this and help you make decisions about the best way to manage your business.
I always say, delivery is as fluid and changing as water. New technologies and methods to fight spam are constantly being developed and innovated. Think about it, an ISPs entire business depends on making sure their subscribers are not inundated with spam. If they don’t do a good job, people leave, and revenues drop.
Currently 72% of the 320 billion messages sent on a daily basis is spam. It will continue to become harder and harder to reach the inbox if you do not get good guidance and expertise, this is one of the main reasons we created mobileStorm Pro.
Read this great article on the future of deliverability here:
http://www.email-marketing-reports.com/iland/2009/10/future-of-deliverability-1-role-of-user.html