We have a customer who have their /32 IPv6 block captcha blocked, and also their /19 IPv4 have been blocked with captchas.
The big issue is that it doesn't help to solve the captchas, there is a new one directly after and solving it gives a new one and so it goes on till you move to Bing do do searches.
Even parts of their netblocks that arn't in use are blocked, and have been for 3 weeks now.
We have tried to contact google, but no one gets back. There is no useful information on how to solve the issue either.
Would be great to have a tool like SPAMhaus or other RBLs, where you as a ISP can see the offending IPs and take care of the problem (if there is one).