How does that make Twitter useless? Silence doesn't mean users aren't listening or that it isn't useful. Twitter is a place for conversation and if one loudmouth (or key influencer/thought leader/great conversationalist) is doing all of the talking and most are listening - does that devalue the conversation?
Apparently, Twitter is working for some - those who get it and use it well.
Proof for my point: Twitter Sells $3 Million Of Computers For Dell
A $3 Million dollar profit doesn't sound too useless to me...