New accounts are rate-limited because of past abuses.
> Twelve attempts later I've solved HN's captcha and created another account so I can comment again.
I'm sorry you went through that. I can't do it in fewer than a dozen attempts, or without screaming, either.
The captcha is a service of Google's and is currently borderline unusable [1]. But this isn't Google's fault so much as that captchas in general are just broken right now. We're using them as minimally as we can. In fact, everywhere the code currently invokes a captcha, it used to refuse to make a new account at all.
We marked your account legit so you won't get sent back to captcha hell.
1. It's telling that the images on their own site don't look anything like the cruel tricks they actually spring on users: https://www.google.com/recaptcha/intro/index.html