Pop-up ads, those reviled windows that intrude on your Web surfing, seem to be on the decline. But don't celebrate yet: New forms of advertising that may be just as annoying and even more intrusive are likely to replace them.

Thwarted by both ISPs and blocking utilities, use of pop-ups has waned over the past year. Internet advertising analysts say Microsoft's decision to put a pop-up stopper into the next version of Internet Explorer hastens their demise, but no one expects them to disappear soon. And new styles of ads, including screen-grabbing full-motion videos and rich media that overwrite the screen, are starting to appear.

Read more: PC World.