Reading through a bunch of stuff including Sean's posts on, if 40%+ of users would be very disappointed if your product disappeared, it's a good sign you have a scalable business.
Most of the talk is on 40% of *users*.
But if I survey all my users, not 100% are going to answer (sometimes a google promotion tab hiding problem, sometimes other things) - so how do you account for non-opens/responses in that 40% number?
i.e. if you have an open rate of 60% and of those, 40% would be very disappointed - is that a good sign or is it a bad sign (e.g. 40% of 60% = only 24% of users)