The definition he gives of Screwdriver Mode is when the temptation to fiddle with the possibilities offered by technology take over from what you are trying to achieve. So for example in a Word document you end up spending ages working with the fonts and layout, distracting from the words in the document. Or whilst spending ages tweaking the settings on your digital camera you neglect to take any good pictures.
Scot offers some other examples of how the temptations of screwdriver mode sometimes take over. Definitely worth a read.