Twitter, allowing users to post from a mobile phone or an IM window, is blogging in its purest and most solipsistic form. The service, created by the founder of Blogger, discourages links, and encourages one-line mood updates. What are you doing? asks Twitter in its catchphrase. The content mix, more cat news than world events, is curiously engaging — like, says one commenter, a largely plotless TV sitcom.