BBC NEWS | Entertainment | Stephen Fry on joys of Twitter
http://news.bbc.co.uk/1/hi/entertainment/7845823.stm

Stephen Fry has become a huge fan of Twitter, a social networking service that thousands of people have signed up to, including many celebrities. He says he now has 50,000 'followers' who give him advice such as how to deal with a bat on the loose in his house...

Video clip. Fry explaining why he uses Twitter.

I've always struggled when other people ask 'What's Twitter?' Now I'm just going to send them this link to a short video of Stephen Fry perfectly encapsulating what Twitter is, how it works and why it's good.