Add a feature where users can opt-in for periodic reports to be uploaded as a private gist, and a link is transmitted to you. GitHub is already a trusted party where Homebrew is concerned, so the loss of privacy is minimal. Users control their own GitHub accounts, so they control of the permanence of the data you collect on them. You can use Google Forms to transmit the links, so your infrastructure is cheap-to-free. For bonus points, encrypt the links with your public key.<p>How does that sound?