Once (in about 2002) I looked at a gallery of annual beauty contest winners - I wish I could dig up this specific contest to link to it, but I think any long-running beauty contest would serve the same purpose. I was curious to watch the gradual shift toward old fashions, and they didn't start to look "off" or out-of-date to me until I got back to about 1991. This kind of pattern-recognition-through-unintentional time lapse has produced far less trivial observations. Charles Darwin supposedly was influenced by the long hallway of a manor-dwelling friend of his; along this hallway were pictures of his illustrious friend's ancestors back through the generations, each of them posing with their hunting dog. The dogs were supposedly of the same breed, but their appearance changed noticeably over time. (Note that by the preceding comparison I do not intend any unflattering comparisons, but rather just to generalize the principle.)
This is my excuse for having adding Less Than Zero and Bright Lights, Big City to my Netflix queue out of curiosity. I graduated from high school in 1992 so the worlds these movies showed (if they really existed at all) would have passed before my time. In a way, I was more curious about the subtle differences between the world now and the world just before I reached adulthood. Of course there are the obvious fashion and technology differences (big hair and payphones), but I thought it was worth summarizing my reactions.
Even minor differences are somehow more jarring in a color movie with relatively recent model cars than they are in a black and white movie. Similarly, a friend once told me she hated reading Austen and the Brontes because she can somewhat identify with their protagonettes, whose self-restricting attitudes seem unnecessary and pointless, but the characters and the world they live in is familiar enough that she can't help but evaluate them as modern women. Reading about the wives of Roman senators isn't nearly as frustrating, because they seem too alien to be evaluated as peers. Critics can't stop talking about the smoking in Madmen. Try reading any novel that takes place in an office in the 1950s; all they do is smoke. Try reading business magazines from the late-80s or mid-90s (every article seems to reduce to one message: paranoia about Japan taking over the world).
The other subtle cultural differences that jumped out at me:
1) The role of women. When I watch movies from the 1940s, I'm not so shocked that women have three possible portrayals (secretaries, wives, or sluts), but in recent films I find it more jarring. Granted, perhaps these two films are not good reflections of what women were actually doing in the mid-1980s, but the women the main characters meet while they're socializing show no sign of pursuing any career aspiration other than modeling. Bright Lights, Big City at least has female coworkers. If it hasn't already been done, maybe there's a media studies project in tracking the career ambitions of supporting female characters over time, starting in 1980. As an aside, if you've ever hosted visitors from an Asian company at an official event, it jumps out at you immediately that there are no female officers or project leaders - they're still secretaries. I personally find this uncomfortable in the same way that I'm uncomfortable getting my shoes polished at an airport in the American South by a black shoeshiner.
2) The treatment of homosexuality. In Less Than Zero, Robert Downey Jr.'s character is turned into a gay prostitute in order to pay off drug debts. While today we would still say that forced sex work of any kind is immoral, there was a clear effort to equate homosexuality with a general decadence and nihilism that seemed strange, watching it in 2009. Bright Lights also has a scene where Michael J. Fox stumbles upon two women kissing who invite him in for the fun, and he reacts with confusion and distaste, rather than the strong interest that many straight American males would likely show today.
3) Coworker etiquette. In Bright Lights, Michael J. Fox's coworker hugs him when he's fired; he was obviously hesitant about it, and the hug is seen later to be connected to this coworker's romantic attraction to him. In 2009, this seemed very prudish and strandoffish.
I've often speculated that the 1980s, when I did most of my growing up (ages 5-15) were a conservative island between the 70s and 90s, because all the hippies and partiers now were old enough to have full-time jobs, but hadn't had kids yet. By the early 90s, that changed, and Reagan's morning in America was over.