The first thing most people tell you about living in another country is that you will experience "culture shock." They are very right. The first thing most people tell you about Mexico is "Don't drink the water." That's also right. The first two things I had to get used to about Cuernavaca were both sanitation-related, and from what I hear that's usually the case worldwide. The water here isn't drinkable, and it's a very new experience for me, coming from a house where I could drink water straight from a spring on our hillside, to have to lug a bottle of purified water with me everywhere. The other sanitation issue is the sewer system. The plumbing in most of Mexico can't handle toilet paper and other semi-solids en masse, so we have to throw our used toilet paper into a garbage can in the bathroom. It's cleaned daily but it's one of those things that most tourists would immediately shelve under "eeeeeeewwwwwwwww." Personally I don't care, as long as it's being disposed of properly it's no dirtier to throw it away seperately than to toss it into the sewers with the rest of your waste. Of course, I have no idea how it's disposed of...
Culture shock is also a big problem because of little things like gestures, mannerisms, etc. It's a different social system down here, and while many estadounidenses can get by without changing their ways, when you live with a family and have to interact with civilians every day it's easier to pick up on mannerisms than to be labeled as a clueless tourista and have everyone make an effort to speak to you in bad English.
Food: Big problems for some people. For someone like me who will try anything (and usually like it), mexican food only poses a challenge because it's a dietary change. For those picky "I only eat xxxx food" people you're better off finding a restaurant (there's a very nice chinese one in town...) and eating out. A lot of my classmates had major stomach problems while adjusting to the Mexican diet. I admit, I had a few days of mild discomfort, but I've adjusted much better than many others. The food here is a lot spicier at times (think salsa of some type with every meal), but it's also a lot less greasy and a lot more natural. Whole wheat bread, corn-flour tortillas, meat without growth hormones or steroids or antibiotics, fruit juice freshly squeezed, natural (unbleached) cane sugar. Mmmmm....
I think I like Mexico. It's hard to get used to taking taxis everywhere and remembering not to drink the water, eat fruit from street vendors, etc, but it's definitely not as much of a culture shock as I expected it to be. I thank my Spanish professor (Thank you, Sra. Parsons!) for that.