I’ve been using the Hover Zoom Chrome extension for a couple weeks now. I am completely hooked. The most obvious benefit is for image searches. I’m constantly putting together reference boards for new designs, so this has been a big benefit. However, as you use it you start to get hooked onto other elements of functionality. For instance, on Facebook I can hover over someone’s tiny profile thumbnail image and see their full profile picture. It’s very handy for comments and posts, so I can get a refresher on who the person is without having to click through to a profile page.
If you’re running Chrome, check it out at the Google Extensions site.