It would be useful to be able to tell a human from a computer when users sign up for apps. A large number of bot sign ups would make it difficult or impossible to find the real users and approve them in a manual approval scenario.
That sounds reasonable. Thanks for considering it and taking the time to help us understand the decision.
It would be even cooler if you can add Google's New recaptcha, far more user friendly. https://www.google.com/recaptcha/
Not currently seeing bot signups but wouldn't want it to be a problem once the site is in production. Currently, I have the signup process automated to encourage a valid email address by sending a complicated URL to whatever email address is given. I haven't found a way to vary the URL between signups, so a valid email would not be required once the URL was known. Even if the URL were unique for each signup, bots can have valid email addresses. I don't have an effective way to mitigate the risk of bot signups suddenly exceeding the record limits for my account resulting in paid users not being able to use the site.
Are you seeing bot activity? We have no record instances of this.