[ZeroGravitas]

In South America, where these stats show Chrome in the lead, the growth seemed to be accelerating up to and beyond the crossover point (the same in the few individual countries where they're leading). What about marketshare particularly should make this unusual or unexpected?

I'd assume some kind of tipping point effect as it becomes "normal" not to run IE and/or to run Chrome that could lead to such acceleration since the barriers to adoption are so low.

[rhplus]

Perhaps there's a distribution deal or popular website in South America that requires Chrome to function best (Orkut?). Or perhaps, as you said, it's just a network effect.