When I buy and inventory books, I always flip through to check the condition and pull out anything that might be stuffed between the pages.  Not surprisingly, I find tons of the usual bookmarks and plane tickets and receipts, but the real gems are handwritten notes like these.  
It used to make me sad to see that someone threw out a book that was once a gift (especially considering how personal and thoughtful some of the notes are), but now I feel glad that someone else can enjoy the book that they no longer have a use for.  I keep them all.

When I buy and inventory books, I always flip through to check the condition and pull out anything that might be stuffed between the pages.  Not surprisingly, I find tons of the usual bookmarks and plane tickets and receipts, but the real gems are handwritten notes like these.  

It used to make me sad to see that someone threw out a book that was once a gift (especially considering how personal and thoughtful some of the notes are), but now I feel glad that someone else can enjoy the book that they no longer have a use for.  I keep them all.