John Gruber has an excellent take on the changes Twitter will be making to the authentication process. More and more Twitter is cramming changes down third party developers throats — the very group of people that helped to make Twitter popular. I for one would rarely use Twitter had Loren Brichter (now employed at Twitter) not made Tweetie.
What Twitter really needs to do is convey reasons why they are doing this, not to users, but to the developer community. They need to show everyone the path they are taking.
Now you may be thinking that I would never say this about Apple, and that they do similar things. That too has crossed my mind, but the biggest difference is that Apple has a track record of doing amazing things. So far Twitter has a track record of acquiring VC funding and changing CEOs. ((Also: dickbar.))
Bottom line: this change is bad and Twitter needs to open up about its reasons behind the change, or prove very quickly that they made the right decision.
(Neither of which I see happening.)