According to Rafe Needleman in an Ad Age (http://adage.com/digitalnext/article?article_id=131655) article.
For me (who became a Twitter user less than a month ago), Needleman may be correct. Regarding Twitter, it is merely an info aggragater; at least that’s the way I use it. Inversely, I rarely visit Twitter except to follow the news of a few people (which is pointless because most of the people I follow supply the same info using other services like Facebook).
Edgy Mama recently mused about it on Twitter (http://twitter.com/edgymama/statuses/959014214): “Wondering why folks want to follow me here when I hardly ever Twitter?” There are other, more efficient services to keep up to date with people in your social networks, but Twitter isn’t one of them.