Customer's becoming advocates is the goal for so many companies.
This is because it shows that your product is meeting their needs and they will tell people about it.
In fact, one of the gold standards of customer metrics is NPS - Net Promoter Score... "how likely are you to recommend the product?" and this just goes to show you how important this is.
But how do you track it's impact?
How do you ensure your customers aren't getting burned out?