When you discover an interesting member on Issuu, you can follow to always get the latest uploads and stack updates. Simply click 'Follow' and you're set. From now on you can see new uploads and stack additions from your Home pages. That publisher's content also have a better chance of making it into your weekly digest mail.

Following someone is a one-way relation. The publisher will receive a notification that you chose to follow, but it's optional if s/he follows you back. 

Note, that you can both follow publishers and stacks.