This is an excellent offering for free, from Google. If you ever find yourself working on a document with someone (ie collaboration) Google just made it easier to do this. Instead of making changes to a document and closing it, then sending it to someone by email, you can share this document if you already have a GMail account. By pressing one button added to your Microsoft Office program, it will update these changes to a document stored in a common folder in your free Google Documents library – aka Google Docs (Note: Private meaning between only you and the person you previously invited to work with you).
Watch this video for details: