Small but effective new GMail Lab feature if you are sending and receiving so many Word and Excel files.
Starting today, you can preview the contents of a Google document, spreadsheet, or presentation right in your Gmail inbox — just like you've already been able to do with YouTube videos, Yelp reviews, and Picasa and Flickr albums. Gmail will automatically detect when you receive a document link and display the name and type of doc below the email.
Official Gmail Blog: New in Labs: Google Docs previews