WordPress.com launched a new feature called "Email Post Changes" that help blogs with multiple authors collaborate better on the same posts and pages. If you turn it on, WordPress'll instantly notify you by email whenever a change is made to a post on your site. You'll recognize the format of the email is the same as post revisions, making it easy to see exactly what has changed.
The Email Post Changes plugin will be updated soon for self-hosted WordPress.org users.
More Info: Email Post Changes support document