I was just reading about the development of the Disk II. Randy Wigginton and Woz worked on it for a few weeks, only finishing up the control software (which negated the need for fancy hardware controllers by using software to read and write the sectors in the right spot) hours before presenting it at CES in 1978. They stayed up all night after setting up the booth to get it done. When they finished, they tried to made a back up copy. And they accidentally overwrote the data disk with the blank. Less than a few hours before the show floor opened, they rewrote the entire control system.

[Flickr via Macrumors via Technobob, Apple2history.org]