A recent thread started by lisa seemen of ubaccess, discussing how wcag 2.0 does & doesn't support cognitive/learning impaired users...

http://juicystudio.com/article/formal-objection-wcag-claiming-address-cognitive-limitations.php

this is a group of users which is very much underserved by web accessibility, this needs addressing and wcag is always going to be key to this.

there is little material out there, i've added my 2p worth to the thread, if you have any comments / resources i'd been keen to hear about them.