Effectively, this achieves the complete opposite of what CAPTCHA does. It's a test that only computers can solve. A much more exciting development in the field

Effectively, this achieves the complete opposite of what CAPTCHA does. It's a test that only computers can solve. A much more exciting development in the field of bot/spam detection is verifying the integrity of the user's browser by comparing the exposed functionality (HTML5 and JS) and quirks to the ones expected for its user-agent header. I believe this is the method that Dan Kaminsky's "White Ops" startup uses.