Interesting post.

A few months ago, I spent an hour at Freshbooks, answering questions for a $50 gift card. It was a really interesting session, and the two poeple running the session did two things right. 1. They encouraged me to think out loud as I explored and evaluated the various screens -- which is something I also heard during my interviews with Google. What's going on inside a test subject's head is really what they are interested in. 2. They knew when to move from just observing what I was doing into the more probing "Tell why .." or "How would you improve .." questions.

It's quite an art to extract the most juice from a willing test subject. And it's vital research for a company to be doing.