There is no use in counting calories (either input or output calories) as long as you are in a reasonable range - and that reasonable range is pretty large.
As Gary Taubes has stated in both of his books and a couple of articles: If you consume/burn an extra 100 calories a day (small candy bar/walk up the stairs) for a year, you will gain/lose 10lbs a year (based on the fact that 1 lb of fat stores 3500 calories). And we know this doesn't work! That's why we're on paleohacks.com and not weightwatchers.com
Why doesn't it work? Well your body knows what's coming in and what's going out, so it adjusts both your hunger AND your base metabolism to keep you isocaloric. Eat a little more? Your body ups the metabolism. Cut some calories? Your body slows down. Do a long workout? You get hungry. Lie on the couch all day? Not as hungry.
What people don't realize is that when your body "ups the metabolism", that really means that it's "getting LESS efficient with its calories". What does that mean? Well if you go back to my thermodynamics posts from a while ago, I talk about what a calorie is in terms of energy. But energy and work are interconvertible in physics, so one calorie can easily be mapped to physical work. 3000 ft-lb of work is 1 Calorie (http://en.wikipedia.org/wiki/Foot-pound_(energy)). That means if you lift 3000 pounds 1 ft, or 1 pound 3000ft (or any product of feet and pounds that equals 3000) you did 1 Calorie (food calorie) of work. So lets look at the benchmark Crossfit workout Grace (30-135lb Clean and Jerks). 135 lbs * 30 reps * about 7.5ft (ground to overhead for a 6ft tall athlete) = 30,000 ft-lbs of work. Which is 10 Calories. Now doing that work out did I burn 10 Calories? No! I burnt more than 10 calories. I did 10 Calories of work, but my body is no where near 100% efficient where 1 Calorie eaten turns in to 1 Calorie of work. In general the rule is that you're body is only 12.5% (or 1/8) efficient. So doing 10 Calories of real work took 80 Calories of food. BUT - and here's the big BUT - that depends on the efficiecy of my body, and that's really easy to change. People with "high metabolisms" are less efficient, it may take them 120 calories to do 10 calories of work. People with "low metabolisms" are MORE efficient, they may be able to do grace and only burn 50 calories.
This is the what I call "The Biggest Loser Paradox". These people wear those "Body Bugs" and count every calorie they put in their body and then they go on the scale and are disappointed? Why? Well they starved themselves and did a ton of work so their body adjusted its metabolism to be more efficient.
All of those Calorie meters on workout equipment? Those just use a fixed multipler of Work Done -> Calories Burnt. I bet it's 8. It's not personalized to you in the state you're in today. How could it know? Only your body knows.
So back to your original question: As long as you're eating a reasonable diet, just make sure you eat enough food to do what you want to do. If you eat too little food your body will "slow down", if you eat too much your body will "speed up" to keep you isocaloric. Now all of this goes out the window if you're having a high-carb diet (leading to metabolic derangement), because even though you're eating, the insulin is stuffing it away for storage, so your body can't see it and burn it. That's why a LC diet works! As long as you're not metabolicly deranged, then just eat to satiety. If you're trying to reverse metabolic problems, then don't count calories, just cut the carbs, up the fat and protein and your body will do the right thing once it knows what signals to listen to.
Edited to add:
Right after I finished this post, I learned about Dr. K's blog. He says the same stuff better than I did here: http://jackkruse.com/jacks-blog/
