So I've heard this thing called "Cairo" mentioned a lot in Longhorn blogs and in other forward-facing Microsoft-related info. What exactly was Cairo? All I can find with a Google search amounts to little more than people saying "omg vaporware lol".

I've heard:

- object oriented file-system
- was originally slated to be NT 4, then 2000, then XP, and now Longhorn
- advanced UI

That's all I can find. I'm posting this in Techoff because I want technical details - what is Cairo from a tech perspective? What sort of scenarios did it enable? What happened to it?