I got the answer to my question. It's called Creators on Spider-Man by Tom DeFalco.

When you say book, do you mean an actual bound book or was it a magazine of some kind?

Thanks, just had a look at the FF one on amazon. Might be worth a look, but it's hard to say. Stan is usually too much the showman to be good at this kind of thing, so that leaves Joe Sinnott as the only contributor from the most important FF run. I would like to read what the under-rated Keith Pollard had to say about his time on the book. And although I wasn't reading the FF by the time they were on the FF series, I suspect Doug Moench, Walt Simonson, and Warren Ellis would all have some good insights into what made the Kirby/Lee run so special. Maybe Ralph Macchio and Mark Waid too - I have mixed feelings about both of them, for various reasons.

This is one of the problems with being a comics fan, as we all know: these continuing characters or series have had so many different people working on them, and every reader will have his or her favourites and, er, whatever the opposite of "favourite" is. I really don't want to read John Byrne's or Jim Lee's comments on the FF, for example. Maybe not even Roy Thomas's, much as I respect his work in general, since I understand that he was responsible for what I think was the ridiculous idea of marrying off Crystal to Quicksilver.