As a couple of you know I've come up with a different approach to this problem - the online PID definition index:
http://rdm.openlighting.org/
This provides a structured way of describing a PID's format in a much richer way than the PARAMETER DESCRIPTION PID supports. Think of it as DDL for RDM.
The big advantage here is that the data format isn't tied to the RDM specification.
I'm happy to export the data in other formats (XML, JSON etc.) for other people to use in their controllers. Other programs can check the last update time by hitting
http://rdm.openlighting.org/update_time
See you all in Dallas.
Simon