Here is a post about tracking data about yourself – make sure to read the comments as well.
I track a few areas of my daily life and I find it extremely helpful. For example, I use My Fitness Pal app on my iPhone (they also have a website to use instead). I enter in the foods/drinks I consume for breakfast, lunch, dinner and snacks, and it automatically keeps track of my fats, carbs, sugar, sodium, protein and caloric intake. It can also keep track of my caloric expenditure as well, at least for cardiovascular exercises. The one thing it can’t calculate is your calorie burn for weight training because there are too many factors to determine that number. That’s the one downfall. Otherwise, it’s extremely convenient for me to pull out my phone, enter in my data, and then I’m done. Easy