Well, with New Years coming up there's no time like the present to weigh in on the supposed end of socially observable time. Gotta get it said before it's no longer relevant. I'd like to disagree with the idea the there's some 20 year turnover period in history during which style or fashion can be easily identified a having turned a significant corner. Consider the suit of clothes: the basic style of a man's suit has gone unchanged for, what, over one hundred years now? Yes, there have been changes, but in the larger scheme of things none of any astonishing note. Look at the suit worn by Italian Premier Vittorio Orlando, second from left, at the Paris peace conference in 1919:

He would look perfectly at home in any contemporay urban setting today. Surface changes have given rise to innumerous little variations such as OMG! wider or narrower collars, or more or less numbers of buttons, but the style remains the same.
Think of a ubiquitous contemporary look like the t-shirt and jeans or khakis combo:

T-shirts were developed in the early 1920's, jeans in the 1850's. But for the last eighty years or so, this style has persisted. All that has changed is the wideness of acceptable venues for wearing it. Now you can wear it to virtually any ocassion, from church to meeting heads of state to high powered business meetings. Anywhere, really.
If you're going to take, for example, bell-bottom trousers as characteristic of how people dressed in the early 1970's, you have to ignore that these were common in the 1920's, and that the vast majority of individuals in American society and the world at large didn't wear them at all in the 1970's. Most people in the 1960's and '70's wore straight legged slacks, and even "hip" individuals had abandoned bells by 1974 or so. But they, like most modish styles, make for an easy bookmark in the visual history of an era. People like to "brand" time periods this way without much regard for the habits and styles of most of the public. You might as well consider the blogging hipster with a hat, black glasses, a scarf and a Starbucks as representative of the last eight years. If it's your desire to brand the '00's with a typical look, that would be close enough. But would that look represent most people you know?
If anything stands out to me, it's the general prevalence of socially observable neoteny, as the totalitarian state renders us all back to infancy. We play little games, drive toy cars around and wear clothing appropriate to the sandbox as we wait for Daddy to tell us what we can do. Children of any era share a great commonality.

^^He's wearing the same outfit he wore just out of diapers.
But it generally seems that clothing styles change along far more glacial lines than casual retrospection seems to suggest. Give it another forty years and see what happens.
To me, it's obvious that cars, clothing, music and lifestyles in this country are quite a bit different and uniquely identifiable (in a small, branded sort of way) from twenty years ago. But in a wider sense, people still use telephones, drive cars, wear similar clothing, and even listen to similar music as they did 100 years ago. Major changes seem to enter history in two ways: verrrrry, very gradually or all-at-once.
My question would be, why is it that so many millenialist articles like this one are popular now? Is it simply a trend of the early twenty-teens?