How strange; I'm pretty sure it's an issue with the latest firmware. I was able to reproduce this issue on a few other units.
There seems to be a solution, unfortunately it is not really documented: http://www.surfaceforums.net/threads/help-with-freeze-on-boot.13741/page-2#post-109851
I see the same issue since I have the SP3 (December 2014). Maybe it is related to exactly the same symptoms I see (not always) when rebooting when docked with the original docking station. (There are also several threads in this forum with similar experiences).
I have never seen these symptoms (stuck at the black "Surface screen") when booting (vs. rebooting) or when waking up from hibernation. When stuck at the Surface screen and pressing the power button for several seconds, the next boot always was successful.