Use the Windows Server “Longhorn” Scenario Voting tool to access a list of 380 validated scenarios over 43 different categories for Beta 3. Customers can use this list to build test plans, access related technical documentation, and send feedback about Windows Server "Longhorn" Beta 3.
The Windows Team invites you to participate in making Windows Server Code Name "Longhorn" the best server operating system ever released by Microsoft. Now you can take part in the evolution of Windows Server Code Name "Longhorn" by testing the featured scenarios with each milestone build and providing feedback. Not only will this give you valuable insight into the product, but you can also influence it through direct input into the Windows Server product teams.
So basically you follow the above link, go to the web page - select the scenario you want or have tested - then comment on the documentation/feature. Sounds a great way to influence Windows Server 'Longhorn' or just get pointed to the section of the documentation you're interested in. Virtualization minded people - I suggest you follow the x64 path - and study the Server Core and Clustering parts (amongst other things).