Ok, I spent some time on the pcb docs. I sent it off to Dan for review, but a preview of the new content is here:
http://www.delorie.com/pcb/pcbfile.pdf
These docs are taken from contents in the pcb source file, so hopefully they'll stay in sync with reality in the future.
I've updated the -cvs version of the manual at pcb.sf.net/manual.html.
-Dan