What is new in this just released, new preview build of Longhorn? Why did Microsoft make it available to the public and why are developers the first to get a look at the new Windows at such an early stage? This short article just published on MSDN nicely sums it all up.
I too get quite a few customers asking me to do a speech on Longhorn for them, not all of them expecting that the story that I can tell them now is the developer story about WinFX, Avalon, Indigo and WinFS, not the story for the IT-pro or the administrator.

Read: About the Longhorn Community Technical Preview, WinHEC 2004 Build (Build 4074)