Google has decided to hide their +1 button within the search results.
Originally, the +1 button was shown next to a search result listing, clear and opaque. It seems that Google is in the process of reducing clutter on their search application. Instead of making their button perma-visible, they are hiding it until the user mouses over the listing, whereby it will be revealed and clickable. Additionally, by mousing over the result, the large grey "more" arrow bar which shows a website preview is also revealed at that same time. Such experimentation is common by the search giant, who makes an effort to meaningfully respond to user activity and test design concepts with a live, segmented audience. Google's preference for simple, clean design and endless refinement of their primary product is highly commendable.