TheOptimizationIdiot - 4:00 am on Apr 30, 2013 (gmt 0)
Injecting code is far different than securing a service with a noindex tag that protects the greater good of the internet community. I see no legal issues with Google restricting their services for lawful acts by preventing their proxies from being indexed and cached. That is the responsible thing to do.
Much like the public registration discussion, this is no solution to the problem. As soon as it doesn't work on AppSpot those who want to do damage to your client's site(s) will go somewhere else, because duplication is indexed by Google and can outrank the original, and it's not only AppSpot duplication.
The solution, in the case of duplication, is Google not indexing/showing duplicates.
"Adding directives" when proxy serving (that's done by adding (inserting, injecting) HTML code into the source of the page or adding (inserting, injecting) server-side headers not specified by the originator -- IOW: Either way they break protocol and inject, (insert, add) code into the original) is not a solution to the problem.
Them caring enough to only show the first discovered version (and if necessary giving people a way to submit content prior to publishing publicly) is, because then copying does no good and people are forced to do something besides steal content to rank and "harming the originator" becomes much more difficult and quite possibly even worthless in many cases.
They really do not need "noindex" on the page or in the HTTP header of a duplicate to not index the duplicate, really, they don't. All they need to do is stop their search engine from indexing duplicates and much of the duplication on the Internet will stop.