One thing I've often wondered about this: who are all these people posting their email addresses everywhere?
Even if I'm reading a blog post I'm so interested in that I'd like to read more later, I would never dream of putting my address in one of those "sign up for more" popups. I know many will comment that it's offensive that they popup over the page, but for me that's not even the main reason - email is just not the right place for that sort of thing, I already get enough cruft in my email account without adding blog post notifications too. I know not everyone is exactly like me but surely that is the rule rather than the exception?