Here's some research from Thad Starner, who is actually the person in charge of the Glass project over at Google: Citation: http://dmrussell.net/CHI2010/docs/p1695.pdf. He studied the performance of people doing a warehouse box-filling task using orders given on paper in a couple of forms, spoken, or presented through a head-mounted display like Glass. Summary was that workers using HDMs are more focused, work faster, and commit fewer errors overall, mostly because they spend less time switching contexts and have the information much more available.