Although sjgadsby answered way better than I could... I just have to say that Tweetdeck - I enjoy it on Android - will invariably not be coming out simply due to perceived market size.

In fact, the Twitter apps like Mauku, Witter and whatnot on Maemo seem to be lacking in a lot of functions that hopefully will catch up to the other offerings on other platforms shortly.

But the good part... the Twitter.com website does work just great.