This was the last straw for me as a Twitter user - I noticed that I'd stopped clicking on links since I had no idea where they went, knew that they'd often get mangled & require manual adjustment, and didn't want to give Twitter more advertising data. I've stopped posting anything with a link there because it's subliminally annoying seeing my posts get mangled when the original url was informative and there are all the same privacy issues. Twitter has managed to raise the annoyance and friction of using it for anything to do with urls enough to kill that off for me and I can't help but wonder how many other people. I know the link text is displayed on the site, but New Twitter is just as annoying as it ever has. Congratulations Twitter - you've started killing off the open clients, you've tried to snoop on every link clicked by a Twitter user, and you've quite thoroughly demonstrated that you've got the determination to keep making things worse. Bye!
You should never see a t.co link on Twitter or elsewhere — if your client is showing t.co links, it hasn't implemented support for entities.