I haven't done this yet, but I've read about it in a book and it just felt like a no-brainer to me. I'm trying to get my act together and find a place for all the exercises that the book illustrates (it's called "Getting Back to Happy" and it's written by Marc and Angel Chernoff) but the very thought of listing my personal reasons for being grateful already made me feel better. I will definitely put those thoughts to paper, maybe in my journal.