Well it seems that twitter wants you to use their app and only their app when you want to tweet. So Plume, ubbertwitter, Twidroid. They want you to C&D.
Now please don't misunderstand that comment, they actually haven't issued a C&D but they have moved to discouraging devs from making apps that might happen to work better then their own. Why? Well there's always only one reason and it's usually green, at least in the USA.
Twitter to Devs: Don't Make Twitter Clients ... Or Else