JP Rangaswami likes Twitter. What's even better is his analysis of why it adds value to our online life despite its apparent deficiencies (e.g. 140 character limit). Before you dismiss this as just another Twitter fanboy, recall that JP knows a thing or two about enterprise IT.
JP hits the nail on the head by discussing Twitter as a pub-sub platform. One of the key features of a pub-sub system is user (client) control of messaging. I choose who I follow on Twitter and thus the messages I receive. I've stopped following people because their tweets weren't very relevant to me. Nothing pejorative in that--simple message management.
This is similar to what people do with RSS readers and the overall feeling is the same. The key difference to me is that Twitter is lighter weight (primarily due to the 140 character limit) and more ephemeral. Further, because I use a desktop client that's always open to follow tweets, I can glance at it from time to time and see who's doing what without much overhead.