On the VisitMix blog:
"During Wednesday's keynote, Ray Ozzie mentioned an exciting offering that we will be making available in the near future through an invitation only Technology Preview program. Click here to log-in to CommNet and start the sign-up process. This special preview is limited to 2000 participants, so sign up soon to ensure your space in the program!
A note for our friends outside of the United States… the first phase of this technology preview is not available internationally. However, please complete the sign-up process and we will notify you as soon as this offering is available in your country."
Given that Ozzie's speech was filled with allusion to mesh and Horizon (mesh is the network that runs across Horizon, allowing users to link their devices for sharing files and folders amongst other things), the logical conclusion is that the internal-only dogfood will be extended to the public.
While this may not be the case, if you went to Mix08, you'll still want to signup now.
Microsoft, Horizon, Microsoft Horizon, Ray Ozzie, Microsoft Projects, Signup, Invitation