I already blogged about Yahoo! Search using Google Gears. Looks like they're using Google Gears to optimize responsiveness of their Search Pad, and they're also doing it only in Google Chrome where there's no HTML5 local storage implemented.
I've just used Yahoo! Search in Google Chrome. I got a typical Gears popup asking me if I want to let the web site use Gears. I still have no idea why Yahoo! suddenly likes using a Google product; neither Google Search nor Yahoo! Search are helpful for several keywords.