How American Non-Atheists view Atheists

Minnesota study
American adults have less tolerance towards atheists than towards people who belong to a different Christian sect or a different faith. A 2006 study performed by the University of Minnesota found atheists to be the least trusted identifiable group in the United States, as well as the group parents would be least accepting of their children to marry.

The study can be cited as: It is available online from one of the authors and by subscription through JSTOR, SAGE, and EBSCO
 * Journal publisher's press release; University's press release;
 * doi: 10.1177/000312240607100203
 * American Sociological Review April 2006 vol. 71 no. 2 211-234

Gallup polls
Gallup has been polling people on whether they would refuse to vote for "a generally well-qualified person for president" if they were an atheist for over 40 years; here is the historical data: (from the "Gallup Polls & Other Surveys" link, below)

The religious affiliations in America are changing rapidly. Between 1990 and 2001 the proportion of United States citizens without religious affiliations apparently rose from 8% to 14% while adults believing in Christianity dropped by 1% per year in that time. (2001 ARIS study; ReligiousTolerance.Org entry on it)  If this drop continues over a generation the United States will change dramatically. Not all without religious affiliations are Atheists, agnostics, or freethinkers, but many are.