I think there is a parallel way the user base evolves: at the beginning, users are selected for by their ability to recognize value, meaning only a small amount

I think there is a parallel way the user base evolves: at the beginning, users are selected for by their ability to recognize value, meaning only a small amount of knowledgeable, early adopers signs up; then (business) customers who are willing to spend real money dominate; finally, people who heard about it from friends dominate. The critical thing is that last group sometimes entirely fails to understand the value of a product, is entirely uninterested in being a "power user," etc, and is happy to keep paying a small fee for fairly low quality.