Twitter.com

Twitter is one of the most hyped social networking sites at the moment. It basically revolves around the simple question: "What are you doing?". You post updates of 140 characters or less, which your followers will receive. You can use twitter with your mobile phone, third party applications or directly via the web.
The micro blogging provided by twitter seemed pretty simple and pointless to me at first, but when you start using it it is highly addictive.

http://twitter.com