I don't have a handle on this yet, because it's become virtually impossible to tell how traffic from Twitter arrives. But the hit counts on my short URLs are going way down. I used to get two or three thousand clicks on each one, as recently as a couple of months ago. Now I get two or three hundred clicks. I don't know what to attribute this to.
I recently started supporting the Twitter Cards feature, so you get a 200-character synopsis of each piece on Twitter, without clicking through.
I'm not sure this is such a good deal. :-)
I'm very concerned that we're turning over all our flow to a small number of companies. And we can't tell whether they're passing our tweets along to everyone who follows us. I'm beginning to wonder about that too.