The Cascade Bicycle Club in the Pacific Northwest threw me into one of these multi-minute Captchell vortexes when I tried to log in to my years-old account to renew my membership and register for one of their organized rides. I was already on the fence as to whether it would be worth paying to do these rides that I have already done several times over the years. That (ironically) dehumanizing experience pushed me over the edge. I didn't complete the Captchas, didn't log in, didn't renew my membership, and didn't register for anything this year.
More and more frequently when presented with a captcha, I've been deciding I don't care enough about whatever it was to want to exchange robot training for access. Especially if they pull that shit after I've spent effort on something (a comment, say) - I will absolutely walk away and not come back.