Google's stars let you save your favorite search results
We already know that people use the search bar instead of the address bar, and they Google things instead of entering URLs -- heck, Google Chrome combined the two bars into one thing. Bookmarks have become a power-user feature, these days. Look at the hilarious-yet-illustrative saga of the ReadWriteWeb commenters who landed on the site via Google -- because RWW had a post that ranked well for "Facebook login -- and thought ReadWriteWeb was a new design for Facebook. They wondered why they couldn't log in!
Google knows that tons of users just click the first result without reading, so the power to change the first result is something that users will definitely take advantage of.