> what on earth can you say in 144 characters of less
> that has any gravity at all ...?
One thing that supporters note is that "re-tweet" is essentially a way of vetting. There are of course millions of new URLs each day, but if people who I trust send me a link, I'm more likely to take it seriously -- and I hope the reverse is true. You see that even here: how many "messages" have less than 140 characters of "content" ...? So "tweeting" can be seen as not just the message, but also the medium: a low-transaction-cost way of building networks of trust. Yes, each of your follow/follower connections must have a different "trust value" but over time this can become a deep, rich network.
Disclaimer: I don't tweet either.
/jordan