I guess Firefox since I live in it more than any other app

Neo Office and iCal, I think. NetNewsWire. Who can pick just one?

It's true. I have just tried Twhirl which I am liking so far, but it is early days.

I use Twhirl myself, and a couple other Adobe Air things. I do like it, but there a few issues, like the limit exceeded thing, which bug me

I liked twhirl a lot but I don't really use twitter that much anymore.