If you wait until your product doesn't suck to launch it then you have waited too long.

Analyze your customer lifecycle.  What is the cost of customer acquisition?  What % quit?  What is the monetary value of a single customer?

CHI - Customer Happiness Index - What is the probability that a customer will stay?  Measure actions that can predict this such was when they last logged in, what features they used recently, etc.

Store all your data even if you don't know what to do with it yet.

Test the advertising of your product before actually creating it.