Twitter has grown from a small Internet curiosity used by a handful of people to America's third-largest social networking site with, as of May 2009, more than 32 million unique visitors each month [source: Wauters]. Not bad for a service that began 2008 with less than half a million users.
However, there's no way to tell how many of Twitter's new recruits signed up to follow their favorite celebrity. In April 2009, Oprah Winfrey began using Twitter, and it had a profound effect on the service. Thirty-seven percent of visitors to the site were new users on Oprah's first day [source: Graham]. There is little doubt that Winfrey's tweets helped Twitter grow an astonishing 83 percent in April 2009, despite the fact that severe lags and outages plagued the service throughout the month [source: Sachoff/Riley].
Sometimes celebrities don't even need to be users of the site to bring it down. In March 2009, the site crashed when Barbara Walters tried to explain Twitter to "The View's" audience. In fact, her comments preceded perhaps the worst outage Twitter has experienced in quite some time -- the entire site was unable to load. Not even the trusty Fail Whale was able to make an appearance [source: Gawker].
If Barbara Walters merely mentioning the site can cause such severe Twitter outages, there's no telling what could happen if a more prominent star began using the service to reveal particularly juicy gossip. In other words, if Bono ever tweets the reason he won't take off his sunglasses, or if Will Smith uses Twitter to explain why he couldn't be both the DJ and the rapper, you can probably expect a significant lag in your tweets -- if you're able to send them at all.