Screenshots of an unknown build of Windows 8.1 have emerged online today, revealing new Start Button and Start Screen changes. What's interesting is that the Start Button in this particular build cannot be turned off, this could all change before RTM however. These screenshots confirm that the Start Button is back in action for the desktop!
Screenshots of the Windows 8.1 Start Screen have emerged also, confirming that it is possible for the Start Screen to use the same background as the desktop. This change is to make the transition from the desktop to Metro more easy for the average user.
The Start Button in Windows 8.1 is designed to take you to either the Start Screen or the Start Screen's App List. Selecting the App List means by-passing the Start Screen and being taken directly to the list of apps, much like the Start Menu does in Windows 7.
Boot to desktop is also available in this build, and does what you expect it to do. However it is off by default, which is unsurprising considering Microsoft want you to start using Metro more.