Content.ly, the firm specialized in creating branded content, did an interesting survey with its readers, and they shared all the methodology here.

The best idea: they've used Mailchimp "star system" (which ranks the subscriber in terms of newsletters opened and links clicked) to split the answers between the users that are engaged (4 and 5 stars) and the "control group." When doing surveys, it's always hard to create a control group and do focused testing, so this is a nice, fast, solution.

Another interesting bit is that they've used the  "Net Promoter Score", a common way among marketers to find out who is your "brand advocate." I didn't find their rate particularly high, but that question (and answer) should be attached to every media kit out there, I think.