A pair of economics students probe the Oprah Effect:
Our results suggest that Oprah Winfrey's endorsement of Barack Obama prior to the 2008 Democratic Presidential Primary generated a statistically and qualitatively significant increase in the number of votes Obama received as well as in the total number of votes cast. For example, a 10 percent change in the county-level circulation of Oprah Magazine is associated with an increased vote share for Obama of approximately 0.2 percentage points. This estimated effect was higher in areas holding caucuses rather than primary elections. In terms of voter participation, a 10 percent change in circulation is associated with a 0.06 percentage point increase in turnout. Similar effects from the endorsement were found in areas with differentially high sales of books included in Oprah's Book Club. In total, we estimate that the endorsement was responsible for 1,015,559 votes for Obama. The 95 percent confidence interval around this estimate is higher than the difference in votes between Obama and Hillary Clinton in our sample. This suggests that Winfrey's endorsement was responsible for the difference in the popular vote in our sample.
I'm not sure book and magazine sales are a perfect proxy for Oprah's influence. But I hope the meme catches on, just so Obama can make a Kennedy/Romney-style speech swearing that he won't be a mindless puppet of the Church of Oprah that elected him.