I've seen multiple comments suggesting HN uses ReCAPTCHA, but I have never encountered it myself, and I even have Javascript disabled and login through 'anonymous' IPs such as tor, so I'm unsure what these users could be doing that is 'worse' to trigger ReCAPTCHAs.
If most users don't even know that ReCAPTCHA is used, that's a good sign that it is being used as little as possible, though.
If most users don't even know that ReCAPTCHA is used, that's a good sign that it is being used as little as possible, though.