Documentation:
HumaniNet's Plone Documentation
http://groups.humaninet.org/about
Humaninet documents their experiences, including lessons learned, custom workflows, a number of how-to documents, etc. There is also some general information about evaluating and deploying open source software for non-profits
 
Documentation at plone.org
http://docs.plone.org/
The primary source for Plone documentation, with RSS feeds.
 

 

 
Useful Links:

 

 
Training:
Plone Magic Camp by New York Zope Users Group
http://www.nyzope.org/document.2006-06-06.86071...
This is a long awaited Plone training in New York. RSVP contact@nyzope.org
 
Session Videos
http://plone.org/events/conferences/seattle-200...
Twenty sessions from Plone Conference 2006 were videotaped. Here they are.