David Blunkett's remarkably discreet confessions are a case in point. Potential purchasers obviously thought that if the papers had all the best bits, there wasn't much point in forking out good money for the rest.
And they didn't.
That old tabloid hand Alastair Campbell drew the obvious lesson from this and declined the serialisation of his diaries -- and sold a lot of copies.
But there's still a problem.
Campbell announced that he had left out lots of juicy bits, particularly details of the Blair/Brown feud, which he had been particularly well-placed to observe.
"I don't want to destabilise the party," said the ever-loyal Alastair (no doubt he's saving the even better bits for the "full" version of the diaries).
The real big one, of course, is Tony Blair's forthcoming opus. I read somewhere that Blair had told Brown that he'll leave this until after Gordon's premiership because he could hardly avoid the question of the vexed relations between them.
Mind you, as he hasn't signed a book deal or a ghostwriter yet, Gordon can probably rest easy.
Which brings us to 'The Ghost', Robert Harris's book about a former Prime Minister called Adam Lang, his formidable wife Ruth and best mate and colleague (and, in the book, mistress) Amelia Bly.
Harris, a former political journalist and once, best pal of the Blairs, denies stoutly that these characters are based on Tony, Cherie and former No 10 "gatekeeper" Anji Hunter.
We all believe him, of course we do. The fact that Lang also found time to involve us in a disastrous Middle East war has got nothing to do with it either. Must mean that Lang was based on Anthony Eden.
Not to be outdone, Cherie Blair has signed a deal for her own memoir, which will major on her thoughts as a civil rights lawyer (wonder how she squares that with her support for the war in Iraq) with some stuff about life at No 10 to keep the groundlings happy.
Cherie, a feisty scouser, is no fan of Gordon Brown, so quite what she leaves in and leaves out will be the cause of much pondering among the political classes.
It will also provoke the odd furrowed brow among newspaper and broadcasting executives (these days a television programme or three tends to accompany big political books), who will have to decide what the memoir is worth to them (Cherie would be well advised to go for a serialisation deal).
But who will buy it? Sadly for Cherie, the likely top bidder is the Mail, which has given her a fearsome rollicking in recent years. Will the Sun or The Times save her embarrassment?
But the big one, as we said, is Tony's oeuvre.
This may be years ahead, but it's easy to predict the two big questions people will still be asking. What did he really think of Gordon Brown (actually quite a lot of people know this already) and precisely when did he decide to go to war in Iraq?
Many people think the decision was taken at his cosy confab with George Bush at Bush's Texas ranch, over a year before the vote in Parliament. Blair has always denied this (as he would) and just lately some of his declining stock of friends have been putting it about that, even if he said then that he'd support the war, what he was actually trying to do was string George along in the hope that the United Nations would somehow or other dig them out of a hole (by shooting Dick Cheney, perhaps).
Actually, this isn't as daft as it sounds. Blair had a limitless belief in his ability to schmooze people and pluck victory from the jaws of defeat. Unfortunately, in this case, Bush proved rather more resilient than even the Ulstermen.
So Tony will have to tell the truth, or something uncomfortably close to it.
Still he can console himself with the certainty that this is the memoir every paper wants, including probably US biggies like the New York Times.
He'd better start finding his own ghost pretty sharpish. My money's on Iraq apologist William Shawcross.