Usability Insights for Product Design Interview Questions

For product manager candidates who need to prepare for product design interviews, reading and thinking about usability issues is a fantastic way to get ready.  I came across a fantastic article titled 5 Lessons Learned from 100,000 Usability Studies.  It includes video and user commentary from actual user tests.  My favorite takeaway: multi-level navigation presents a problem, partly because of visibility issues and partly because it requires precise mouse movements.