For most of my products, I've had customers before launch. Then again, I guess that depends on what you mean by "launch". I've never been big on showy launches. I usually put something up right away, and then get to work refining and finding more customers. Based on my last couple endeavers, I no longer even begin work on any new products until I already have a customer for it. (and by "work" I mean actual coding/design/development, because of course the process of finding a customer for a new idea is still technically work of the non-technical variety)