Hardware revisions and user upgrades

How do I know which revision my 301 hardware is? What are some differences between the two most recent revisions? And finally: what are the prospects of the hinted at user upgrades - how are these expected to work? Many thanks!

Everyone has the same hardware revision: revision 7. It is silkscreened on the back.

The user upgradeable part of the hardware is the red CPU/RAM board on the back. When an upgrade becomes available, you would just pull off the old CPU/RAM board and push on the new one.