Silicon Valley Insider points out this morning that Oprah — after making her grand debut on Twitter two weeks ago — hasn't tweeted in four entire days. In her most recent tweet, which came last Friday, she asked popular helicopter-jumping Wolverine star Hugh Jackman out on a dinner date for tomorrow night, before his appearance on her show this Friday ("Hugh ... I'm countin' the hours. Wanna do dinner the night before. Same booth? Or catch up fresh on the air"). Jackman accepted: "Dinner Thursday night, our same booth would be perfect." But then he tweeted, cryptically: "I am going to work on getting to Chicago sooner. Cannot wait ... " And now, for nearly a week, Oprah's been too exhausted to tweet. We wonder what happened!