Usage
Subject: Usage
From: Karen Lancaster <lancaster.karen@gmail.com>
Date: 5/7/10, 12:33
To: Barrett Brown <barriticus@gmail.com>

Non-believers is much the preferred term in terms of incidents of usage over unbelievers:
(Aren't you glad you have such a good editor?)
 
http://query.nytimes.com/search/sitesearch?query=non-believers&srchst=cse
 
http://query.nytimes.com/search/sitesearch?query=unbelievers&submit.x=14&submit.y=5