Currently when writing a message on our own profile, we are limited to 140 chr. and when typing an indicator shows us how much space left we have. But when writing on someone's else profile, or even while replying to comments, that indicator is "missing" (it's not even coded, in fact).
I think it could be great to display it everytime.
By the way, it might be more user friendly to display the textarea like Twitter does, I think (ex: http://j.ungeek.fr/d71e95e)