I do. I use it to monitor my calories, protein, and sugar intake. I use My Fitness Pal which is an app for the iPhone and iPad. They also have a website so I can print out what I ate for the week and compare it to my mood charts and see how what I ate affected my mood.
I find that the food journal helps a lot. It makes me feel more accountable to what I eat. So if I feel like I want to sit down and eat a huge bag of candy, I'll have to look at the glaring red column in the "sugar" category. Then I'll feel bad, so I won't eat the candy.