Users around the web are reporting that Google's showing them full-page previews when hovering over search results, akin to search competitor Bing's own preview function.
There's been a "Page Preview" search option for a little under one year now, but this implementation is automatic and provides a lot more vertical glancing. Google often tests out feature ideas with a select group of testers without announcing it officially, and that's what it looks like here. Are you seeing the page previews in your results? Are they helpful, or just one more piece of noise on the page?