<A target="_blank" href="http://www.webmonkey.com/blog/Gmail_Features_Graduate_From_Labs_to_Big_Leagues?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+wired%2Findex+%28Wired%3A+Index+3+%28Top+Stories+2%29%29">Google claims the features were selected based on "usage"</A>. I guess this means YouTube previews are more popular than Google Docs previews. The new features include attachment detector, search auto-complete, and vacation dates.