As a tool, Twitter has its advantages and disadvantages, but does it really matter if Oprah Winfrey decides to keep up with her account or not? Apparently the Silicon Alley Insider finds it fascinating, even tracking the number of people following her and the rate of new followers compared to other popular folks on Twitter.
I don't pay a lot of attention to entertainment news, but since Winfrey's activity on Twitter is making the news I thought it'd be good to point out that this is a pretty poor metric for the success or failure of an online community. Whether Winfrey (or a ghost twitterer) is hitting Twitter to tell us all about her shopping sprees or lunches with other celebrities.
Likewise, how many followers a single person can attract is a pretty lousy metric for community health. Having Oprah on Twitter may have driven a lot of people to the service initially, but it's whether they talk to one another -- not Oprah -- that matters.