Initially, I am going to try to focus on what the other reviewers have not covered well. I will update this review with more details as time permits.
It feels light and comfortable to hold when folded like a book. The grip is nice and not slippery at all. It will not readily slip out of your hands when folded and held from the hinge side.
It feels steady in laptop mode. You won't flip it over by just writing with a pen. You have to push harder on the screen to lift the keyboard base.
The detached clipboard (screen) is thin, very light and almost feels like holding a clipboard. With an i5/i7 CPU, that's an amazing feat.
Keyboard is great but not as awesome as my ThinkPad X1 Carbon keyboard. It gets close though.
The hinge is firm and built solid. But keep in mind that you can't open the display all the way flat because of the hinge design. It will stop about halfway past upright (my guess is about 45 degrees or 135 degrees from closed position when facing from front). You can however detach and flip it and then close it with screen facing up.
Also, if you want to write on the screen in laptop mode, you will need to hold the screen with one hand for stability and comfort. You could do simple diagrams without holding the screen though.
I have never had Surface Pro line before so I don't have any benchmark to compare to. I compared the OneNote pen experience with Surface Pro 4 and Surface Book and felt that Surface Book was slightly better (but this could be just an illusion in my mind). I feel that the Samsung Galaxy Note 4 phone pen is more accurate/precise when taking notes vs. the Surface Pen. Surface Book pen was very usable but not perfect in my mind. When I wrote "Hello World" multiple times in cursive at the normal writing speed, the letter "l" was about half the height of what I had expected. I had to slow down or put more pressure to get full height. Maybe there is a setting to adjust pen sensitivity that I didn't try.
The magnet to attach the pen is fairly strong. It will not fall off from just shaking the device. But you can knock it out with some force or while taking it out of a tight backpack.
Pen Eraser is fantastic. Feels just like a real pencil eraser.
TouchPad is great. Feels smooth like my MacBook, my ASUS ROG and my Lenovo X1 Carbon. No issue with the TouchPad .
The front facing camera quality was very good and it adjusted for low light. The back camera was good but showed some fuzzy artifacts (around the objects) if I pointed towards fast moving objects.
GPU (NVIDIA GeForce & Intel HD 520)
Surface UEFI Boot Menu
Surprisingly, the video driver froze/crashed few times during my 30 minute hands on with Surface Book. I was able to reproduce occasionally by quickly detaching, re-attaching, flipping, closing, detaching and reattaching. Here are a couple of screen shots of what I encountered.
This is the reason I didn't pre-order today but I am hoping that this will be resolved soon.
So would I buy it? Yes, in a few weeks.
Questions: If you have any questions, ask in the comments section below and I will get the answers for you.