Engaging the early users in a dialog is the best way to keep them motivated. Don't just email them (though, do that) but given them something to look at like a

Engaging the early users in a dialog is the best way to keep them motivated. Don't just email them (though, do that) but given them something to look at like a rough demo video, or a screen mock-up that helps explain the concept (and offer an email for feedback), or something they can do to find out more.