This is a fascinating post by Joshua Giardino @techaritys on “Why a Search Giant decided to build the Fastest Browser ever…” http://ipullrank.com/googlebot-is-chrome/
This is why you’re seeing annotated screenshots in Instant Previews of the Google SERPs. The instant previews are in fact an impressive feat in that they not only take a screenshot of a page but they also visually highlight and extract text pertinent to your search query. This simply cannot be accomplished with a text-based crawler.
and why SEO Cloaking has nowhere to hide from the the Google Bots