Although I'm mostly interested in programming I like to read very good questions and answers from other areas as well.
A network-wide newsletter could contain:
- top questions from the stackexchange.com "hot questions" feed (I'm currently following that one in Google Reader, but it's hard work)
- announcement of new sites from Area 51 (at the moment, I have to remember checking regularly)
- network-wide announcements (basically blog.stackoverflow.com)
- content from the new site blogs
- more interesting things I didn't think of
What I would like best is to be able to customize my newsletter (e.g. "I want to read all hot questions from Unix, but only the very hot questions from Cooking"), but I realize that would probably be too much work and possibly cause confusion.