In fact it doesn't really kill usability (at least not for me)- I didn't yet cut out holes for buttons, and for simple reading I wont need them - if I come across a situation where I need anything else but the centerbutton for reading I will.
Actually I picked a notebook with extra stiff covers and I have to say I'm positive they are even more stable than all the tin-dvd-covers I came across so far.
The idea was to find something that is as safe as tin-box and as easy to use as a normal cover - besides that I hope that it does reduce the chance of pickpockets snatching it when they decide to peek into my bag
