Up to you whether to accept the conclusions of this article, or Everett's reply, or the reply to the reply (all linked from this site):
http://ling.auf.net/lingbuzz/000411
Everett himself debunked Everett. Originally he said Piraha was recursive. Then he changed its mind and said it wasn't, thus, all of Chomsky's theories are wrong. He learned to speak Piraha training to be a Christian missionary, not as a linguist. His talk here was with a conservative author, not a linguist.
Everett was chair of the dept of languages, literatures and cultures at Illinois State and former chair of the linguistics department at university of pittsburg...