Some people think that usability is very costly and complex and that user tests should be reserved for the rare web design project with a huge budget and a lavish time schedule. Not true. Elaborate usability tests are a waste of resources. The best results come from testing no more than 5 users and running as many small tests as you can afford.

This article is from the year 2000 (queue Conan O’Brien’s side kick), but it’s filled with timeless goodies. Its conclusions are a straight forward example of diminishing returns, but worth reading how they arrived at them from empirical evidence.