As far as overall traffic not falling off I can understand that. I close them so fast I forget which sites use them and so it never enters into the decision making process (will I go back) for me. I do find them annoying and have never signed up for one. I'm MUCH more likely to signup for your newsletter or follow you on twitter if you put links/forms to do so AT THE END of the article.
This is what I've done with my newsletter form and it works pretty well. It would likely be possible to get some more signups by adding a popover form but I'd be doing it at the risk of annoying readers that would have never signed up.
I have noticed that some sites make the popover happen when you mouse off of the window to the back button, which kind of makes sense because you're leaving anyway.
That's largely why I don't think it harms many people. It's a bit of short-term rage by those who care, many people close them out without a second thought, and even more people actually subscribe than a form in the side nav or end of the article.
