The Startup Pyramid
This also links to this great article by Marc Andreesen on product/market fit. Basically, you know you're on your way to achieving procudt/market fit if you hit this metric:
I ask existing users of a product how they would feel if they could no
longer use the product. In my experience, achieving product/market fit
requires at least 40% of users saying they would be “very disappointed”
without your product. Admittedly this threshold is a bit arbitrary, but
I defined it after comparing results across nearly 50 startups. Those
that struggle for traction are always under 40%, while most that gain
strong traction exceed 40%.
Hopefully Noopsi is somewhere around that 40%, we get a lot of positive feedback saying they love the site but it is probably time to "officially" survey the users.