I appreciate you posting this, you can also use tools my favorite being convert kit right now, to tag your subscribers. Then you don't have to create a list based on an activity, but just create a tag. For example maybe they're "interested in podcast creation", then use automation rules to send specific messages related to creating podcasts. tag them based on a link they click on in the email.

--Michael Babcock, coaching blind entrepreneurs on how to bring their business online, taking care of the technical shit so you don't have to

http://yourownpay.com/our-blog/