Twitter have been changing the way that other companies link in with their API. This has shown itself in a number of ways. First, LinkedIn stopped being able to post Tweets on their pages, then Twitter forced Instagram to remove it's feature to find friends that are also on Twitter, now they've done the same thing to Tumblr.
I don't use LinkedIn much, so I can't say that that change has had a great effect on me, but Twitter removing the friend-finding feature for other services has made those services worse. Especially on Instagram, where I would check every few days to see if there was someone on Twitter who recently opened an Instagram account. I imagine that whoever's calling the shots at Twitter thinks that's just fine. They've got rid of these damn freeloading services that are using their information and not giving value back.
But I think that's where they've gone wrong. I like following my favourite people across multiple services. I like to read someone's blog, follow them on Twitter, see their Instagram pictures. Now Twitter has broken a way in which I used to link these things together, it's made those services just a bit worse, and (this is the important bit) that includes Twitter itself.
Often I'd follow someone on Twitter, and although I'd be enjoying their Tweets, they wouldn't be blowing me away. Then I'd happen to follow them on Instagram or Tumblr, and I'd find in that medium, they'd be amazing. They'd find great photos on Tumblr, or they'd take them on Instagram, and it would make their Twitter stream seem suddenly more interesting.
So, Twitter, I'm sure you think you're being all clever and keeping all this 'value' you think you've created all to yourself (insert maniacal laugh here), but you're not. You're just making your service worse, and less important to me.
And before you ask, http://alpha.app.net doesn't solve this problem for me, since all of those brilliant people I'm talking about? Most of them still won't pay $50 a year for a service they currently get for free.