I very much enjoyed a month "at home" -- though I use the term loosely since my time in the US included Maryland (+ Ocean City), Virginia, DC, Pennsylvania, New York and California.
Whenever I go back, I see things with new eyes, from a slightly different perspective after having been away and living in another culture. One of my biggest "culture shocks" this time had to do with clothing. I'd become so accustomed to the drastic temperature changes during the day in Mexico, that for the first few days I kept bringing a sweater with me because "it was going to be cold later." After carrying and never wearing the sweater for a few days I remembered that summer at home is hot and, while the evening is slightly cooler, it's a relief and not chilly/cold. It took me a while to feel comfortable/normal wearing shorts again as well.
Also, when I go out in the evenings in Mexico (to a bar, dancing, etc), I usually wear jeans with a nice top or if I'm going with a group, maybe a dress/skirt that goes to about the knee. I do this to fit in with the norm (granted, in certain neighborhoods known for being more trendy/expensive you'll find other styles) and to avoid drawing any more attention to myself than I already do as an American in Mexico. When I went out the first time in Maryland, I wore something I would've worn in Mexico-- and was surprised to see all the girls in short dresses or miniskirts!
Being in Mexico, I've pretty much gotten used to being the American among Mexicans (or other Latin Americans in my program). Going home, it felt strange to be surrounded by so many people that looked like me. One aspect I enjoyed about my visit to NYC this time was that I didn't feel like a minority or a majority. There's so much diversity, I was just one of many colors/ races / ethnic backgrounds.
I did see the US as being very consumer- driven. Granted, I partook in some shopping myself and it's not to say that certain parts/ classes of Mexico's society aren't consumer-driven as well. However, it stood out to me in comparison to my day-to-day life in Mexico (and mostly as an UNAM student).
As usual on visits though, I did enjoy being more familiar with where to go or who to call when I needed things, a more organized and generally more efficient society, being able to drink tap water, etc.