Twitter may be the rage on Capitol Hill, but the American public at large is not yet sold on the microblogging site, according to a new poll.

Only 15 percent of Americans believe that Twitter is an important new tool for mass communication, according to a new 60 Minutes/Vanity Fair poll conducted in late August.

Much larger numbers of Americans cast doubt on Twitter's usefulness, or were otherwise unfamiliar with the social networking service.

Thirty-nine percent said Twitter is a fad that will fade away, while 43 percent had either heard of it but didn't know what it is, or had never heard of it.

The national poll of 1,097 randomly selected respondents was conducted Aug. 27-31.