The most beautiful Android application I have used to date is the brand new Twitter app. Last night I fell in love with the new app, created by Twitter itself -- and really, that's kinda crappy since I feel like I'm cheating on a company I really really like: Seesmic.
Rumor has it that Google will be including Twitter stuff into their Android API for Froyo (2.2) -- which will make it extremely easy for applications to tap into this functionality. If that turns out to happen, developers will rejoice (except Seesmic and Twitdroid of course).
As a developer, you must currently roll your own Twitter client if you want to incorporate that type of functionality -- and with a host of independent Twitter applications, it's impossible to create an app that hooks into Android's intent system effectively.
Applications should be able to reuse an already installed Twitter app by saying "Hey, i want to post a tweet" to the Android OS, and have it launch the user's default Twitter app to perform that operation.
I'm really looking forward to Froyo!