Earlier this month, Google released Instant Previews. On the whole, I think most people like them, but there are many people who don't like them. There is no good way to turn off instant previews without turning off Google Instant.
Until now that is.
ArpitNext created a script for Firefox and Chrome that disables the Instant Previews from showing up on your Google search results.
So if you hate them and you use Firefox or Chrome, install it.
I monitor the forums and I see tons and tons of upset searchers over the instant previews. Again, I think for the most part, people are happy with it. But if you are not, you can not remove them.
Forum discussion at Google Blogoscoped Forums.