For various reasons I've been doing statistical analyses on word frequencies in a number of languages lately, and I found a pattern that differentiates different dialects of Spanish that struck me as curious enough that I asked Gerardo, my test lead from Mexico, about it. I was working with Spanish corpora from Spain and from Mexico, and I noticed statistically significant patterns that differentiate the usage of vosotros and Ustedes across the two varieties of Spanish. The frequency of vosotros in the Spanish corpus was actually about two hundred times greater than it was in the Mexican corpus, for corpora of the same genre (i.e. corpus type difference does not account for greater/lesser presence of second person writing).
I had heard anecdotally that people don't use vosotros in Mexico, and come to think of it I noticed this when we traveled there last spring, kinda -- I mean, pretty much everyone talked to us formally anyway, so I didn't have a lot of occasion to pay attention. Still, I had no idea that the generalization of Usted/es to informal speech patterns was so far along in Mexico. So now I'm wondering whether there is anything pragmatic associated with the use of vosotros for Mexican speakers of Spanish, apart from the obvious not-from-around-these-parts marking. I don't have time to follow up on the corpus analysis on this point in detail, but I'd be interested in reading about it if someone else has.