I paid off $35k worth of student loan debt within 3 years of graduating. While I was in debt, earning more to pay it off was a great motivator. Now that I'm debt free and have my basic living costs covered without worry, more money just does not motivate me anymore.

The most depressing comment I read on HN was one guy telling a story about a sales manager he knew that encouraged his sales people to go into debt so they would be more motivated to earn more and therefore, make more sales.