Here's a good article by internet retailer about personalization in email.

Among [the trends] is the use of dynamic content and special customer appreciation offers. "Email offers an incredible opportunity to build a dynamic conversation and unique user experience, but only if you leverage the data, intelligence and expressed preference of your customers,"

This is one of the things that we are trying to get acros to our customers, and we have made it really easy with our email application server. Our email personalization engine allowed us to rewrite an email application that was several thousands of lines, into under one hundred lines.