Let's assume that Oprah's reach is strong enough and far enough to get her demographic to plunk down their eight to 12 dollars to see Precious – the Oprah Effect in full effect. (You can find out where and when Precious is playing near you on the official movie website.)
I'm not talking about critics and journalists or the people in big cities who like to participate in a friendly Oscar pool or want to be up on what was in the New York Times. They're already seeing the movie in droves; it made $1.8M in limited release its opening weekend. The latest numbers I could find on her demographic are from 2007, back when people were wondering if Oprah could help get a president elected. (Answer: Yes, she can.)
According to Nielsen via MSNBC, "Oprah's audience is predominantly female, white, and over the age of 55. Nationally 7.4 million people watch Oprah daily -- about 2.6% of American households. Four percent of American women (about 5.7 million) watch her daily, compared with 1.2% of men (1.7 million people). Overall, 2% of all 18- to 49-year-olds watch Oprah."