"We had to spend two months writing the whole billing system up; Chargify and those services didn’t exist at that point. So, if we wanted to have recurrent billing we had to write it ourselves and do all the logic"

If you implement a new service out of necessity to solve a problem you have at work, it is a very good indication that service is also needed by other companies. Instead of using this service you created internally only, you should release it and see if there is a great demand for it.

I think this was a missed opportunity for Wufoo to create another great service.