My own tiny neighborhood ISP thinks they are smart and have their own CDN for caching everything under the sun. Of course it doesn't work well, not only it caches DNS and HTTP requests like kids collecting candy in Halloween but it also breaks HTTPS sometimes.

As an anecdote of how bad ISP caching can hurt you, I am a web developer and I was debugging an issue in a legacy system. I had fixed the stuff and deployed a new version. Erased all the caches in my machine, refreshed the page, broken. I thought that maybe I fixed the wrong thing and started fixing more... now rinse and repeat over five hours before you realize that the cache is happening at ISP level and that things are fine in the live version on the real internet. This ISP is called PredialNet, web developers from the city call it PredialCache...

I know this is about DNS and not HTTP but their cache servers will also cache DNS requests, so moving some domain to a new machine and IP is also a quest under their network. For a while I paid PIA so that I could side-step their cache servers.