The best Twitter interface, in my humble opinion, is (currently) Hahlo a web application designed for the iPhone that uses the Twitter API to offer an alternative skin for the service. There's a lot I like about the way Hahlo approached the UI. So much so, that I started missing those features when Twittering from the desktop.

That's where Fluid comes in. I'm certainly late to the game here, but Fluid is a pretty handy little Mac application. It allows you to create Site Specific Browsers for web applications you use. These SSBs are then available as a dock icon or menu bar item, as if they were standalone desktop applications.

Each SSB has its own preferences and User Agent settings, and they're conveniently untethered from your main browser of choice, able to be command-tabbed to, and unsusceptible to browser crashes caused by other sites. Fluid uses Webkit for its rendering engine, which enables it to work with iPhone web apps.

It rocks in combination with Hahlo, but also for other often-used web apps. Thought I'd mention it here for other potential late-to-the-gamers.
Use Fluid with other apps? Do tell.