Twitter Redesigned (screenshots)
fastcompany.com
fastcompany.com
Another big thing is that the ecosystem is feeding back into twitter.com now. Apps aren't just built on top of what Twitter puts out, but Twitter also pulls that information back in. This has a lot of potential that goes beyond what Facebook can do with it's walled gardens.
The paradigm indicated by the deeper content view - like pulling in full Flickr sets - is encouraging. I'd love for it to include the full text of linked articles, for example.
As this matures, I'll definitely consider using it in its own Fluid app - like I do with Gmail, Lighthouse, and other web applications.