Sure - Amazon is one - they allow you to see past orders, comment on products,place new orders, perform returns, etc. all through their collaborative system.
Service firms could do something similar - allow clients (and even prospects) to have access to a secure portal where they could see project information, tasks, read and leave notes about the project, access project documents and collateral, review time (if you are so inclined) or task status (if you don't track time), make requests for changes, approve proposals, see past invoices, pay past invoices ... the list goes on from there.
To me that is Collaborative CRM. Basically SocialCast + CRM + ERP + firm management in one easy to access portal.