Any idea whether this affects (randomized) A/B testing? I think that in the past, Google has simply ignored the dynamic test changes to the site's content. Now I'm not quite sure anymore.
As of when I left Google in 2010, the JavaScript random number generator always returned 0.5 (and some SEO figured it out and blogged about it, no secrets here). However, I was trying to convince my manager to let me instead seed a random number generator with an HMAC of all of the currently loaded HTML and JavaScript (to make it deterministic but hard to display something good 1 in a million times but 100% of the time to Google's indexing system).