I completed a large fraction of my thesis by speech, including coding and LaTeX. While there are tools to help with coding (there used to be many knowledgeable people at http://tech.groups.yahoo.com/group/VoiceCoder/, but I'm not up to date since my condition has improved) I wouldn't want to wish it on my worst enemy. I'm amazed that Hawking has te patience to function like that, he must be an extremely driven individual.