According to the Google Docs Blog today, they’re introducing the ability to control access to documents at the page level:
Using page-level permissions, you can make some pages private for certain users while keeping other pages public for everyone to see. For instance, let’s say you have a Google Site that you’ve shared with your team and your manager. You can allow your team to see one set of pages, let your manager edit another set of pages, and keep yet another set of pages private for only you.
As is usually the case with innovations, they’re not available right . . . [more]