My current project involves interacting with a chat bot. We could require users to sign up on a form and make sure we have a boatload of data from them upfront before opening up the service to them.

Instead what we do is tell them to add a bot to their buddy list and send it a greeting. In doing this, they've already engaged in the service, and we have created an entry in our users database based on their buddy name and chat network. They can then decide whether supply additional information.

There are lots of ways to lower the barrier to entry if you're willing to change the way you think about online services.