I'm currently developing a bot protection testing tool - BotMeNot (
https://botmenot.com/) - and one of the most commonly implemented anti-bot measures is reCAPTCHA.
It's a relatively efficient way of blocking out bot traffic. However, it's believed to sometimes come at a price of being too annoying for the real human visitors.
I wanted to get ProductHunt's take on this. Has a CAPTCHA task/riddle ever been too annoying for you, so that you've actually left the website and started doing something else or went to another website with the same functionality.