Share 'Celebrities on Twitter: Your thoughts?'

What's everyone think about celebrities jumping on the Twitter bandwagon? While Britney Spears is getting all the attention today, I've stumbled across everyone from William Shatner to Dave Matthews to my local Bay Area favorite, MC Hammer. Even Penn Jillette has tweets. What do you think of the whole phenomenon? Do you follow any celebrity Twitterers? P.S. My favorite Twitter semi-celebrity...