Twitter announced on its official blog that starting from August 31st, its API is going to be changed. All third-party clients/applications are now logging on via OAuth, a new method of authentication that doesn't require them to store your username and your password anymore (this has the purpose of increasing users' security). This new change requires some changes in all third-party clients/applications, changes that the guys from Twitter say that they have been done.
They say that most clients, such as Echofon, TweetDeck, Twitterific, Seesmic, and Twitter for Android, iOS and BlackBerry are already authenticating through OAuth, which is not true. TweetDeck, Seesmic and Twitter (all on Android), are all refusing to sign in. I've last checked a few minutes ago, and there is no update into the Market (for any of the specified apps) to fix this problem. Bad, very bad, Twitter!
If it's necessary, I can make a video for Twitter (or for any other company providing third-party clients for Twitter), proving that the mentioned clients cannot connect at all.