Public Policy Polling provides evidence that MLS still has a long way to grow as only 14% of respondents consider themselves fans of MLS. They did not ask about soccer as a sport or other leagues.
Today the independent polling firm Public Policy Polling its second annual poll of American sports fans, focusing almost entirely on the "Big Four" male professional leagues (NFL, MLB, NBA, NHL) plus MLS, NASCAR and golf. MLS was the least popular of these leagues/sports with only 14% of the 1,222 respondents (a combined sample of landline phone and opt-in internet) said that they are fans of MLS.