The main variables are the length of the beta testing and the involment of the beta testers community. If you provide good support and listen to their needs, 1

The main variables are the length of the beta testing and the involment of the beta testers community. If you provide good support and listen to their needs, 10% is not unreasonnable but giving good support can be very hard, depending on the size of the community. I would use 1% as a basis -assuming the service really serves a need- and go up from that, depending on the available resources for support.