Mine got stuck at 7%. I left it to it's own things and it eventually just told me that there was an error resetting, and from then on out i just got a continuous boot loop.
Did you find a solution to this? I bought my i5 SP4 a few days ago and basically cannot get it to work anymore. It updated to the November update and after that when booting it would log me in to a black screen with a tiny bar at the bottom and no buttons would respond. I tried to reset it, first via the built in recovery and then via a USB drive, but I am no stuck in a boot loop. The resetting takes ages and then just ends with "there was a problem resetting" and nothing else for me to do.
Q - how do I reformat the drive? I have not gotten an question about this when selecting to reset the SP4, regardless if I wanted to only reset all files or clean it up properly (the option that can take "hours").
Frustrated ... guess I will have to return it for a new one if I can't fix this.
I tried the beta graphics driver, and it seems to have made a substantial difference. I'm still having the occasional glitch but it does seem better after installing the beta driver.
I seem to have resolved my issues. First I had to use the MS support site to download and use the Surface recovery image which basically restored it to factory defaults. Applied all the updates, except November TH2 as MS had pulled it at that point. Surface seems much more stable - no longer seeing the annoying graphic freezes and have only heard the audio pop once since. No blue screens yet either. Have since applied the November update on top of all the others and things seem to be okay.
On a side note I managed to knock the pen off whilst carrying it and unfortunately the nib hit the floor and bent it - wish MS had included a cap! ;-)