Journaling is the important part. It takes tweaking. The scale, at the end of the day, is the most honest thing you've got. If you're meeting your goals, then your food intake and exercise level is right. If you aren't, then you either need to adjust your goals, diet, or your exercise! I don't pay much attention to the calories MFP says I burn, and I've adjusted and tweaked calorie goals and continue to do so. I try to stay in that 1-2lb / week lost range.

Like Dos says, it's sort of a myth that a calorie is a calorie (or if you wanna be really pedantic, a kilocalorie or kCal. What we're calling a "calorie" is actually a kCal, which is 1,000 calories.). Calories in and out does matter and the calculations are actually pretty ballpark for most people; but you still need to be eating a healthy, balanced diet. Calories come in Carbs, Protein and Fats. A diet low in calories but that is primarily carbs and fats is going to be less successful than a balanced diet that balances appropriate amounts of all three.