book journal??

Just wondering, has anyone ever thought they should start a book journal i.e. where you write about books you have read/are reading? If so, for what purpose?

In my latest fad of non-fiction reading, almost every page holds some fact I find so astonishing or fascinating or otherwise enthralling that I *know* I will forget at some stage. Every night when I read I think to myself, "OK, tomorrow I will start the book journal." But then I don't, because the next day it doesn't seem as important.

Is it important? The facts/stories/arguments will always be there in the original book(s), but then I will have to rememeber which book it was. And trawl through all the pages trying to find the interesting fact on orchids or embryology or Siberian fox genetics. I guess the reason I never seem to get around to it is that I don't know if I'll ever actually refer to the journal for anything in the future. But the action of writing it down will probably make me remember it more anyway.

Does anyone else share my non-important quandry?