I had a quick chat with Dynamics POS program manager, Michael Griffiths, at Convergence 2009 about the roadmap for Microsoft Retail Management System or what will become Dynamics POS 2009. It sounds like version 2009 will be a major facelift to the current RMS. It will combine the current RMS and POS products into one product call Dynamics POS 2009. This product will be out (nothing official) July 2009 timeframe. The other good news is that Microsoft is going to try to get on a more regular release cycle for the POS product.
The bad news is the great inventory level integration between Microsoft Office Accounting and Microsoft POS will be dropped. Also there is no inventory level integration planned for Dynamics GP and the new Dynamics POS product. If you want inventory level integration it is being planned for Dynamics AX. (For GP there is a basic GL level integration)
There is a 3rd-party Dynamics GP to POS integration:
(not sure it does Dynamics POS 2009 though)
microsoft rms dynamics gp moa pos integration