In the introductory chapter of The Vanity Fair Diaries: 1983-1992, today's Tina Brown weighs in on young Tina Brown, and her verdict is clear: from day one, she was hot, hot, hot. Her work for The New Statesman right after university? "Frisky." Her 1977 affair with the "fearless, crusading" Harold Evans, whom she'd one day marry? "A scandal."

Her old college flame Martin Amis? A "literary lothario" who was "small and Jaggeresque."

After all these years, she still writes in Vanity Fair display type.

I'm not sure who green-lighted these opening pages, which blunder so frequently into self-parody. At times, Brown seems capable of writing in only two registers: brag and humblebrag. I prefer the straightforward brag - at least all the brass horns are playing in the same key - though I do admire how she twice manages to reveal, by Page 10, that she was quite shapely in her youth, both times under the guise of a complaint.

But! After this fusillade of boom-boom and hype, Brown's book - an edited version of the diaries she kept while presiding over Vanity Fair - begins in earnest, looping back to the early 80s, when she was still her younger, less-assured self. Watching her settle into the confident, industry-conquering editor she'd become is a revelation. So is the glimpse she offers into her own habits and appetites. Brown is a woman of wondrous drive and ambition, arcing through the world as if fired from a cannon. One might think that people of such vectored determination don't stop much to think about it. But Brown's diaries reveal surprising ambivalence.

"I want more time to contemplate," she writes in 1989, "but I can't seem to live any other way. I feel panic when I stop."

Most unexpected may be Brown's many entries about the hazards and psychological challenges of editing while being female. Media reporters and male competitors routinely trivialise her accomplishments. Never once during her tenure does she work up the nerve to ask for a proper raise, even after Vanity Fair becomes profitable and Harper's Bazaar starts to court her. (She eventually enlists the help of a superagent.) Even she suffers from a self-esteem gap.

When Brown was first offered the job to rescue the recently revived (and incompetently revived) Vanity Fair, in 1983, she was just 29 years old. The magazine was an outpost of confusion in those days, and Condé Nast was a castle of paranoia, its towers filled with schemers hoping to avoid defenestration.

It took a while for Brown to master the politics of this byzantine kingdom, and it took a while for her to arrive at the formula that would ultimately be responsible for the magazine's success: a mix of celebrity chronicles, foreign reportage, true-crime stories, profiles of power brokers and extravagant photo spreads - all sitting side by side in the back of the same limo.

For legacy-media freaks, The Vanity Fair Diaries is a bound volume of crack. Brown's moment wasn't just predicated on the excesses of Wall Street. It was predicated on the excesses of the magazine business, of a time when editors still had time and money to burn.

A crisis in Brown's world was being seated at the wrong table at the Four Seasons, or being forced to coordinate coverage of Andy Warhol's death by speakerphone because the person best suited to do it was off in Gstaad, Switzerland.

Yet after reading these diaries, I still wonder how much of an audience exists for them. Pages upon pages are filled with stories about dinners with doyennes who, even in their day, were only a big deal in one or two ZIP codes. Many of its barons are long forgotten, dead or disgraced. The dish about Condé Nast's kings and queens regnant will be tasty to those who know them, but will anyone beyond their own (dwindling) clan even care?

Tolstoy can ask you to remember hundreds of characters. I don't think Brown can.

To me, Brown's truest and most heartfelt confessions are about her maternal guilt and ambivalence. She's beset by fears that her jet-engine work drive will never be compatible with a sane family life. "The weekend was hard, with G"   - her toddler son, George - "being very difficult and Harry chained to his computer as bloody always," she writes in 1989. "Two workaholics don't make a rightaholic, particularly when it comes to raising kids."  

Knowing that her son has Asperger's syndrome - Brown has written about it in recent years - makes certain entries especially painful. Gradually, we see her realise that her son is perseverating, mixing uneasily with other kids, missing crucial developmental milestones. Before he's properly diagnosed, a neurologist chalks up his differences and delays to his premature birth. "Was it my fault for working too hard and long?" Brown asks herself. Your heart dissolves. It's so hard to imagine a high-powered father asking himself this same question.