UPDATE: Gizmodo got the official word from a Twitter spokesperson that UberTwitter “violated Twitter policies and trademarks in a variety of ways.” Like “a privacy issue with private Direct Messages longer than 140 characters, trademark infringement, and changing the content of users’ Tweets in order to make money”
The issue with UberTwitter is probably the name. Twitter doesn’t like applications using official Twitter terms in their name, like “tweet” and especially the word “twitter” itself. (That’s why TwitterFon became EchoFon.)
Via Twitter support
Regardless of how you access Twitter, we are dedicated to making Twitter better, faster and more reliable for you. As part of this effort, we ask applications that work with Twitter to abide by a simple set of rules that we believe are in the interests of our users, and the health and vitality of the Twitter platform as a whole. We often take actions to enforce these rules.
We have suspended UberTwitter and twidroyd for violating our policies:
Every day, we suspend hundreds of applications that are in violation of our policies. Generally, these apps are used by a small number of users. We are taking the unusual step of sharing this with you because today’s suspension may affect a larger number of users.
We are committed to helping you continue to use Twitter during the disruption of these applications. You can download Twitter for Blackberry, Twitter for Android and other official Twitter apps here. You can also try our mobile web site or apps from other third-party developers.
Read support topic here