It's not the countless tons of newspapers and magazines that were devoted to her, or the thousands of Web sites that, even now, are churning out tens of thousands of pages on the topic of her amazing life and tragic death.
It's most certainly not the spammers, e-mailing offers for Diana memorabilia.
It's bigger than that - the very nature of communication media, the very phenomenon that has itself gone from horseback to satellite, has utterly changed. It happened slowly while we were distracted with the very events those media convey.
Many commentators called Diana's death a defining moment, in the way John F Kennedy's assassination in 1963 was. In the case of JFK, writes Hotwired's Jon Katz, we realised that television had grown up and become the medium of record for important events.
In the case of the Princess of Wales, I, for one, believe the revelation is that all media have fundamentally changed, as have we, the media consumers.
Old-style media was about the record, the news, the facts. In days when the media were few, imperfect and relatively slow, only the most pertinent facts moved to, and were featured in, newspapers, newsreels and early radio broadcasts.
Media space was scarce, its use at a premium. Big news events were nothing short of the declaration of war, market crashes or the deaths of leaders whose very names were synonymous with whole nations struggling through their darkest hours.
Readers and listeners, battered by generations of war and economic decline, wanted most news that, it was hoped, could help them steer towards a future of plenty and peace.
The Internet has added near infinite capacity to a planet already wired for thousands of television channels, where global networks feed thousands of publications distributing millions of copies. In 1997, gigantic oceans of information wash ceaselessly across our planet.
This vast media capacity has created a perpetual, global, slow news day. There just aren't enough affairs of world-shattering import to regularly fill all the media, all the time.
Media consumers of the 1990s, buoyed up by 50 years free from global war and widespread economic ruin, are focused on the challenges of daily life in a world that is becoming ever more complex, at an ever-accelerating pace. Modern media organisations desperately seek ways to create compelling content that interest this increasingly well-informed, and media-jaded public.
The stakes are huge - commanding the interest, and thus the eyeballs, of a large part of humanity, is a highly marketable commodity. Corporations will pay huge sums to place their advertising before reliably large and alert populations of potential buyers.
Into this space came Diana, Princess of Wales. Her story blossomed, expanding from its fairy-tale beginnings to fill the ever-growing media capacity. Editors struggling to fill space found in turn a royal fairy tale, courtship, marriage, children, Palace intrigue, infidelity, disillusionment, divorce, depression, bulimia, personal triumph and reincarnation.
Her life became one of the most durably interesting stories of all time - 44 covers in America's People magazine alone. Diana became perfectly mediagenic, and was always painfully and joyfully human.
Her struggles and triumphs were a modern, serial parable for a bewildering, complicated world where things so often don't work out as planned.
She wasn't President, Prime Minister or Queen. She didn't cure cancer or invent the Internet. Yet, she became part and parcel of our late 20th century lives.
Diana's saga was such a perfect match for the maelstrom of media bandwidth that her life and its coverage became ever more entwined. Media interest grew and fed upon itself, enlarging her to mythic proportions. Legitimate media began covering her like tabloids, and tabloids pushed to almost obscene lengths to fill ever more space in more sensational ways.
And that didn't change when her life and two others came to a tragic end in a Paris traffic tunnel.
Every media outlet on the planet covered her death and funeral, and most of the people who could, half the planet's population, watched, or listened or read or clicked the hyperlinks that traced her last journey.
The coverage of her funeral briefly united the planet in silent grief, perhaps one of the grandest memorials of all time. Her loss also brought great anger directed at the very media to which we clung, never more eager for the messages, nor more willing to kill the messengers.
I, for one, will always remember the power of those moments when a whole planet stood unified, even if in grief. Would that this glimpse drive us to dedicate our thousand channels always to a connected, united humankind