Email is a well known acquisition and activation lever - but it can be particularly powerful as an engagement driver... which in turn drives activity and potential conversions. Below are two examples of weekly emails that arrive from consumer web services Apture (a web toolbar that I have installed on this site) and Yardsellr (a social classified site and Dogpatch Labs graduate). Both emails are automatically generated, highly personal and visual. Apture's email contains weekly reports and charts for various pieces of data associated with your website's readers and their interaction with the Apture bar. It is very informative and simple to digest - but most importantly, it conveys if and how Apture improves your website (time on site, searches, etc)... and because they are confident it will, these email reports drive loyalty:

Yardsellr's "activity report card" delivers weekly and all-time statistics about your Yardsellr account and active listings. In addition to being colorful and full of useful data, these emails are actionable: users can edit / cancel listings, generate traffic virally (ie Twitter and Facebook) or upgrade listings for additional traffic.

Best Practices:

We often think about email as a way to drive new users, deliver announcements, or move products / sales. But consider your active users too. Craft personalized, visual emails that are regularly delivered and sum up users' sitewide activity. It is a powerful way to convey the value you are providing while encouraging ongoing activity (upgraded activity too!).