"Pop" is too kind a term. What usually happens is that the screen darkens, and an animated box will slowly scroll into view, then the ad will fade into the box, followed my more JQuery-ish transitions before the close gadget (if you can recognize it as such) finally comes last. Click the close gadget, and the whole thing proceeds in reverse. Really nice when combined with paginated content!
Once I see a page darken, I immediately hit F5. If it darkens again, I close the window. There are actually some sites on the Internet where I intentionally disable AdBlock, but I won't tolerate any site that attempts to block content on purpose.