You don't need to go far to find a frustrated computer user. Often it will be because they find the interface difficult to use. Designing good interfaces has become an important industry, and successful products often depend on having excellent interfaces.
This activity explores just how hard it is to get things right.
Try Engineering has an activity called EEEEK- A Mouse! which explores the concept of how engineering solved the problem of human/computer interface. Students disassemble a mouse and explore the movement on the X/Y axis that determines mouse positioning. Students explore design enhancements to the mouse over time, and as a team of "engineers" add further enhancements to current mouse design. Download Full Lesson Plan and Student Worsksheets.
CS4FN has the following online activities/articles that demonstrates concepts in HCI: