I StumbleUpon often and I have noticed a strong correlation of useless content to pages that have pop ups. Almost every page that I have looked at, has had silly stuff.
So to save myself time now, I just ban domains that have pop ups. I might miss some good ones, but I also miss the overwhelming junk.
I hope marketers are listening, because people are using programs like Adblock to avoid your messages. You have to provide something compelling to a web surfer, not just a call to action. Most of these pop ups are saying something like increase my popularity on other social networking or subscribe to my newsletter. How about letting me read your content first so I can judge?