[feralchimp]

If you don't have a way of "doing anything with" your customers that functions independent of holding their email address and/or credit card number, you're not doing something "with" them so much as doing something "to" them.

Not every application needs to be a goddamned community experience wherein the original transaction spawns a lifetime of subtle sales attempts from the developer. Be happy that someone paid to use what you built. If you want more money from them, or you want their email address, build so much cool shit that they want to hear about what's next.

As Chris Rock said: "You pay to see me? We cool."