These are the same captchas they use on Gmail for registration and what not.
It does nothing but ask for captchas over and over?
Without the 'back link', it cannot redirect you to your original search. Your 'from location' is google.com/sorry, so, once you pass the test, it sends you back to google.com/sorry instead of back to your previous activity which triggered the Captcha.
Wouldn't my referrer point back to this HN page?
If you're coming from an HTTPS page (which I think HN forces) to an HTTP page, the referer is not sent. It is only sent for HTTP->HTTP and HTTPS->HTTPS (even cross-domain, despite the info that leaks out)
Same here @ work. Might check again when I got home.
Are you using tor?
Nope, I'm not using Tor or anything like it.
This seems to happen sporadically in the morning at my company and I speculate that it's due to a large number of employees who are querying Google at the same time from the network's IP. Google sees this as bot-like behavior and shows the capthca.