New leaks have shown that the Windows 8 public beta, the Consumer Preview, will take the risky step of dropping the Start button in the conventional desktop. As shown on PCBeta's forums, later pre-release builds now just have the app shortcuts, running apps, and taskbar. The menu will still be available, but users will have to mouse to the relevant corner to bring it up.
It's not clear why Microsoft would be hiding the Start option in the conventional desktop. Most users won't need to see it as they'll go to the Start screen in the Metro interface. Microsoft might be aiming for some consistency, since jumping back to the Start screen with a mouse uses the same concept of an edge gesture.
As a beta, the preview release due late February isn't locked down and has room to change before Windows 8 is released to manufacturing, most likely sometime in the second half of the year. Any change may depend on how the interface change works in practice and how testers react.