Popover ad when mouse leaves browsing window

I've seen a new ad movement where the user is on a website and they decide they want to navigate away. So they move the mouse outside the web page to click a bookmark or type in a URL. But they're attention is interrupted by a popover window!

Sometimes this can be annoying but I saw a really good implementation of it. On the LA Times' website they offer 4 weeks for 99 cents. Nice deal. But I don't want to subscribe today. I'll shop on Amazo...What? A window just told me I can get 8 WEEKS for 99 cents!

That's an awesome way to close the sale when someone decides to pass on the initial offer. As this seems to be a trend I would think it would benefit BLOX customers. So is that something any of y'all could use?