signor_john - 5:36 pm on Feb 8, 2009 (gmt 0)

Ask.com have be doing the preview thing for like the last year, can't say people find it that great as they are not getting any market share.

1) Ask.com's implementation is pretty weak, and it's almost invisible to casual users. (The user has to click a binocular icon, and the resulting preview pane doesn't show much. It isn't the equivalent of the default mouseover behavior in Brett's "imagine this..." scenario.)

2) Ask.com has such a tiny market share that most searchers have never been exposed to the binocular icon, let alone to Ask.com's small preview panes.

Still, your guess is as good as mine. But Google won't have to rely on guesswork--it will have test data to guide its decisions.

BTW, as far as opt-in vs. opt-out goes, I'd guess that, if Brett's scenario were implemented, it would be opt-out, because opt-in wouldn't provide a critical mass of previewable search results. Of course, if Google wanted to be evil, it could sell a "mousover preview" option in organic SERPs, just like the optional boldface business listings in the White Pages of my local telephone directory. :-)