Got my Surface Book yesterday. Runs smoothly. After spending a few hours updating the firmware and everything else, Windows Hello works pretty well. The only pain is that Windows Update wouldn't update the firmware. Actually had to search around and do everything manually. Not hard, mind you, but still annoying.
The screen is pretty spectacular. The new n-trig pen works very well, much better than my old Wacom pen on my Thinkpad x220t. The keyboard is very solid. The magnesium casing is extremely solid. Definitely better than aluminum in terms of feel and strength.
Biggest negative so far is the fact the rubber feet might be a little too thin. That might not sound like a big deal, but I'm wary of leaving a big scratch on an expensive table. (I go to a lot of houses and use the computer on a lot of expensive tables.) I might actually pick up some 3M rubber buttons to protect things. The problem is it seems the fulcrum hinge might be the scratch causing part which makes it more difficult to protect against.
As far as software and normal teething problems...I haven't had any. All in all, that's a good start. We'll see how things work out in a week or two. So far so good though.