I use it a few hours a day, a few times a week exclusively as a virtual display for my macbook.
Being able to put a huge virtual monitor anywhere is the killer feature and I don't tend to use it for anything else. It's indispensable on flights where laptop lids can't even fully open.
Apple got the interactions just about perfect for AR window management, etc.
Of course the main drawbacks are the weight, size, and overall embarrassment from having a giant face computer strapped to your head.
I don't find it very comfortable for more than a couple hours at time, at least with the solo knit band + the belkin head strap. I'd like to get a dual knit band at some point.
But when this sort of hardware gets miniaturized I think many people will prefer it to hunching over a laptop screen. Just like headphones, wearing glasses while typing at a black screen could signal "Do not disturb, I'm working here"
[0] Steve Jobs on Virtual Reality (D3, 2005) https://www.youtube.com/watch?v=bQECSInWVPY