Just to set expectations, Teiid is not the same as MetaMatrix - see http://www.jboss.org/teiid/about/history.html. If you are looking specifically for MetaMatrix documentation, start with http://www.jboss.com/products/platforms/dataservices/ and consider contacting sales for more information.
As for Teiid, we will be posting an updated doc set for the up-coming 7.0 release shortly, but if there is something that you can't find there or on the wiki, let us know.
Although they both have the same core functionality, there have been huge changes between the MetaMatrix product and the current state of the Teiid project in regards to implementation/configuration/management. Much of the MetaMatrix documentation would be misleading to you. Can you be more specific about what information you want to know about Teiid?
If it's the MetaMatrix product you're interested in, you'll have to contact Red Hat for info.
Thanks for your answers, I now better understand the differences between Teiid and Metamatrix.
I'll first focus on Teiid Documentation, and contact Jboss if I'm looking for Metamatrix documentation.