Is that the same method used to display the "binocular" views of websites on Ask.com now?
If you haven't seen the Ask.com search results in awhile, check out the ones with a little graphic of a pair of binoculars. Mouseover the graphic and an image of the website appears in a little display.
Here's their faq page about binoculars...
http://sp.ask.com/en/docs/about/binoculars.shtml
I can think of some interesting uses for that effect.
Simon