Chatter-related FAQ

Chatter FAQ
http://www.salesforce.com/chatter/faq/

Chatter Plus FAQ,
https://dreamevent.my.salesforce.com/help/doc/en/salesforce_chatterplus_tipsheet.pdf

Chatter Messenger FAQ,
http://www.salesforce.com/chatter/messenger/faq/

Chatter Communities FAQ,
http://www.salesforce.com/chatter/communities/faq/