This is actually quite dangerous. You can use GData to load the document retrieve all contributors and authors.

You can also retrieve the viewers using a cronjob.

GData returns a "Person" objects in 3.0 http://code.google.com/apis/gdata/javadoc/com/google/gdata/d...

and when you know that google docs generates a revision for just clicking around you can retrieve all revisions and email addresses using http://code.google.com/apis/gdata/javadoc/com/google/gdata/d...

Anyway, it is a great idea... but really not a good idea to use a google doc :-)