Google Scribe is a new Google Labs project that offers keyword suggestions in an open text box, as you type. It is not the Google search box, it is a standalone text entry box for auto word completion suggestions.
You can click on the suggestion or type the number referenced to auto-complete it.
Google Operating System blog goes much deeper into all the features. It seems to only work in the English language.
Obviously, this may come in handy for SEOs who are looking to write better content and even expand their keyword list.
Forum discussion at Google Blogoscoped Forums.