Last night I hashed out the Driver Capability and Driver Property stubs on the Player wiki. They now contain some explanation of what both features are, and some example code to implement both features on the driver and client sides. Both of these features are quite compelling, and go a long way to help deal with run-time driver configuration using Player.
Another exciting new Player contribution: Paul Osmialowski recently contributed a Guile driver to allow Scheme-like scripting from within a Player driver. The driver is well-documented, and he was also kind enough to complete a writeup on the wiki.