I don't know, but we suddenly have them at McDonald's here. Every hispanic I know personally here knows English fluently. What I'm trying to say is that it's a good bet that 80% of immigrants can speak at least some modicum of English (in order to get around the subway, use a blowdryer, or order at McDonalds), but probably 70% of those who KNOW this level of English PREFER to speak Spanish and will use Spanish every chance they get BECAUSE IT'S EASIER. That does not demonstrate a desire for assimilation, nor does it demonstrate a desire to become FLUENT in English.
I speak Spanish as a second language. It takes effort, though, because it's my second and not first language. I spent a week vacationing in Mexico a few years back, and out of respect and courtesy, I spoke Spanish every chance I got. It was mentally EXHAUSTING, and I vowed that my next vacation would be either in a place where I didn't speak the language or in a place where English was spoken (such as Jamaica) so that I wouldn't have to put out so much effort.
Is that attitude okay when I'm vacationing on my dime and trying to just be a vegetable on a beach and get a week of rest (I even downgrade to reading cheesy romance novels during these weeks rather than the political books I read at home)? I think so.
Would that attitude be okay if I were looking to make my RESIDENCE there? I don't think so.
If you do go to jamaica, check out reach falls. It is a bit out of the way but WELL worth it.