Updated 11:33 a.m. PDT with new @Oprah follower statistics.
The official answer is in regarding Twitter Chief Executive Evan Williams' teasing tweet Thursday about Friday being a "very big day": @Oprah.
Oprah issued her first tweet around 7:10 a.m. PDT Friday--the same day Williams and Twitter's top celebrity, Ashton Kutcher, will join her on the show.
"HI TWITTERS . THANK YOU FOR A WARM WELCOME. FEELING REALLY 21st CENTURY," she said, in etiquette-trampling all-caps.