On the latest episode of Build and Analyze, Marco Arment and I speculated that Microsoft would allow for booting past the "Metro" UI, but the latest beta is blocking this capability:
Rafael Rivera, coauthor of the forthcoming Windows 8 Secrets, said he has verified that users cannot boot straight to the Desktop in Windows 8. With Windows 8 test builds, users could create shortcut that switches to the Windows 8 Desktop. Those who didn't want to boot to the tiled Start screen could schedule this shortcut to be activated immediately after a user logged onto Windows 8.
Some other users were holding out hope that Microsoft would allow administrators to use Group Policy to allow users to circumvent the Metro startup screen. But Rivera told me he believes this also is blocked.
It's always possible that Microsoft will reverse this decision later, or that it's simply missing from the latest beta.
I'm sticking by my prediction: Microsoft will eventually allow this.