Was playing with the Surface Book in the Las Vegas store (across the road from my hotel) for 10 minutes.
Must admit, I personally loved it. Couldn't see any major wobble and I was deliberately trying to make it wobble, by picking it up and shaking it round. Of course, it wobbles a bit more than normal notebook with a thin screen, but it wasn't bad. The shop assistant said it was a preprod model.
I kept removing the 'clipboard' section. Around 4-5 times. Caused the computer to crash. Hopefully it is only associated with preproduction. The clipboard section is insanely light. Keyboard was pretty good too. Tried to look at the systems specs, but the computer had an admin password. Also you can connect the power cable to the clipboard section via the connector that connects it to the keyboard section. Oh and removing the clipboard, there's a nice click and you can see the clipboard section 'shudder' as it's released.
Also liked the SP4 - it's significantly lighter and the new keyboard is much nicer than the SP3. I own the SP3. The magnets seem to be much sturdier.
Pretty sure I'll get the Surface Book i7/256GB, either when I'm back in the US or if it gets released in Hong Kong. Also played with the 950XL. They didn't have the 950. Will get that as well only because my 930 screen is now discolouring and dying.
Some pictures: