Ma'am Darling, Craig Brown's book about Princess Margaret, is a simple idea, brilliantly done.
Everybody who ever met Princess Margaret remembered the experience, in the same way they might remember bee stings and other unpleasant experiences. Furthermore they all mentioned it in their memoirs. Therefore you can put together an interesting biography from all these encounters.
For instance?
Cherie Blair, trapped with PM at some do, reaches for Chris Smith, Culture Secretary and first openly gay government minister. "Have you met the Culture Secretary, Ma'am? And this is his partner."
PM: "Partner for what?"
CB: "Sex, I suppose, Ma'am."
You'd be hard-pressed to find a book more choc-ful of awkward silences, deliberate misunderstandings and "get your coat" moments than this one.
I also like the fact that it's a reminder of how there's nobody more star-struck than the stars.
Alan Bennett goes to visit Russell Harty on his death bed. The nurse has to laboriously remove all the tubes and breathing apparatus that are keeping him alive so he can tell his friend something. When she does Russell gathers all his strength and says "Ned Sherrin had lunch with Princess Margaret the other day and she asked about me. Twice."