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Its called content locking, but it is really surprising to see Google testing it out, if it is indeed Google
but if Google figured out how to clean it up, remove the shady elements of it, and make it as non-intrusive as possible - I'd test it out
Hey I just ran across this - looks like you saw an early version of this (I don't think it's related to AdSense though)
Sites showing Google ads should be easy for users to navigate. Sites may not change user preferences, redirect users to unwanted websites, initiate downloads, include malware or contain pop-ups or pop-unders that interfere with site navigation.