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I'm sorry Simon but you have reached the extent of my knowledge on the topic. Many things can only be answered by a Google employee...who can't answer because of a non-disclosure agreement. Our sources of Google info are primarily Matt Cutts, official Google announcements and the occasional response shared by a Google employee on their forums. I would agree with you that Google is quite capable or reading and executing javascript if they want to. I plan to perform a lot of various testing in the future and this sounds like a good candidate. In the mean time, I'd welcome any additional knowledge or experience others can share on this topic.