This is a really good article on why otherwise intelligent people can’t use a computer. The author estimates only 5% of the population in developed countries has high computer-related abilities, and only a third of people can complete medium-complexity tasks. For reference, one of the difficult tasks was to schedule a meeting room in a scheduling application, using information contained in several email messages.
I am somewhat insulated from this in a software company, but I remember the dark days of helpdesk in an architecture firm. I helped people under 25 put a CD in a tray.