Monitoring your Net Promoter Score, or NPS, is done by asking all your visitors how likely it is that they would recommend your product/service to a friend or colleague. It's an easy way of picking up any trends around waning (or increasing) visitor satisfaction. NPS can also be used to benchmark your business against others in your industry.
From stuff.co.nz - an article on the Net Promoter Score, a simple way for businesses to collect massive data
NPS benchmark report for New Zealand - A free report detailing NPS benchmarks for a range of New Zealand industries