It seems to me that the CyBook isn't robust enough for the purpose for which it is sold.
I can't see where the Bookeen site alerts potential customers to the fragility of the device; and they sell it without a cover (suggesting such protection isn't essential).
People aren't breaking their screens deliberately, and yet it seems the device can't withstand a relatively trivial knock.
I haven't had any problems with my CyBook so far, but I treat it far more gingerly than any other mobile device I own. If I'd had the same experinces as some of those reported here, I'd conclude the fault is in the design, and the CyBook isn't really fit for the purpose for which it's sold.