As a librarian, I don't normally condone vandalizing library books. I admit, though, that it can be endearing at times.
Exhibit A: "Save Time - Write Book Reviews IN the Book"
It's hard to tell if this was the work of a single vandal or two offenders (results from the handwriting analysis are still pending). I also have to wonder why the kid didn't join a book club or write a blog or tell a librarian about loving this book. However, his/her literary enthusiasm is still appreciated.
Exhibit B: "Gettin' Territorial"
'Nuff said. This kid knows what's up. (Bonus points for writing in pencil).