The
sharing functionality in SharePoint 2013 has been improved and made easier. In
the upcoming SharePoint Online 2013 (currently still in preview), you can make
use of it already, as described here by Microsoft.
http://sharepoint.microsoft.com/Blogs/GetThePoint/Lists/Posts/Post.aspx?ID=673
http://sharepoint.microsoft.com/Blogs/GetThePoint/Lists/Posts/Post.aspx?ID=673
