I think that I hate contextual text-based popup ads almost as much as I hate those stupid Flash animations where a truck drives around your web browser unless you can find the tiny word "CLOSE" in 6pt light grey text that they've hidden somewhere on the page. You know the Flash ads I'm talking about.
I only see these text-based popups on tech-related sites, so perhaps some of you aren't familiar with them. I can't imagine that they're even half as useful as a regular text ad, but that's besides the point. The problem is that they fill the page with green underlined land mines, and if you happen to move your mouse over one, as I tend to do a lot while reading, suddenly you can't see what you're trying to read anymore. You have to click the tiny X button, and may Internet Explorer have mercy upon your soul if you miss and click the ad instead.
At least the horrid Flash ads usually come up right as I'm starting to read something, not when I'm already in the middle of reading it.