This page contains information about developing new plug-ins for GDesk.
It also contains the first version of the GDesk Plug-In Development Kit.
The kit consists of information required to build plug-ins along with a sample plug-in which is the full source for the InfoView plug-in.
If you manage to produce something interesting/useful please post a link to it here, ideally with source code so that others can learn from your work!
Here's the kit:
GDesk Plug-in Kit