One person's gimmick is another person's killer feature. Say what you will about the usefulness of the convertible nature of the Surface Book, but it is thoroughly and competently engineered (unlike some other entries in this space). And if people find a competent convertible to be useful, they'll buy it.

I see that as gimmick too. I have a surface pro 3 and barely use it as a tablet.

As a superlight-no compromise-unlimited budget laptop there was sony's z series, which I really miss. It had everything, including an RJ45 port, 4 cores i7, two SSDd in RAID and was significantly lighter than this thing (just over 1kg). The only thing it didn't have is good speakers.

It depends what you're comparing it to.

I enjoyed using the iPad as a tablet for watching videos or casual web browsing (typing in URLs or searches on an onscreen keyboard is OK), but found the keyboards available to be utter crap.

The Surface works great as a tablet and the keyboard is great on flat surfaces -- I can use it on a train or plane with fold-town tables, no problem. But if I am lying on the couch and try to type on the keyboard, my belly is too jiggly and does not provide an adequate surface. I am hopeful that (once the software bugs are ironed out) the Surface Book will work in that use case, while still being tiny and tablet-like.

Could I just use a laptop sometimes and a tablet sometimes? Sure, but then I'd have to have two devices I carry around instead of one.

It is without the pen and OneNote. Now it is a legitimate feature that people legitimately buy a Surface to have.

I see people in meetings sitting there and jotting away in OneNote all the time. It is very useful when you project one and then use OneNote as a "whiteboard" of sorts.