I've worked on software that attempts to estimate the end-user demand represented by a given resolver. Most of the specifics are covered by NDA, but suffice to

I've worked on software that attempts to estimate the end-user demand represented by a given resolver. Most of the specifics are covered by NDA, but suffice to say that it's surprisingly difficult to do accurately. There is a lot of non-standard behavior in various resolver software, some of it avoidable, some of it not. This trick of altering the hostname of a subresource to identify the client is a thing I long wished we could do, but sadly we didn't have enough control of the content to do that.