"I reckon most Windows users use no more than 5% of the facilities provided"
It's actually known in the industry as the 80/20 rule, i.e. around about 80% of the user base of any piece of software (operating system or application) use only about 20% of its functionality, the other 20% of users having no need for the remaining 80%. Millions of people use Excel every day to track things like their bank accounts. Accountants also use it to create balance sheets for company audits, all of that good stuff. Little more than rows and columns of figures with the most basic of functions is required for this. About 80% of Excel users will have probably never heard of Poisson confidence intervals, yet there they are.
http://www.kanbancoding.com/2013/08/27/the-8020-rule-as-applied-to-software-development/
BTW, I didn't Google that... ;-)