There is one caveat, however -- the person that's limited by the expiry date can only have view access. So if you want to given them permission to actually edit a Google Doc, you'll still need to go in and lock them out the old fashioned way at the end of the project. Still, for enterprise customers this should be a useful tool, and one more reason to consider Google's productivity suite over Microsoft Office. We just hope this eventually rolls out to all Google users, and not just those with Google Apps accounts.