The more I run, the lower my heart rate stays. The lower my heart rate stays, the less I need to eat to offset. I do 35-45 MPW and eat 2000cal/day, everyday, regardless of what I burned. I never trusted the calculation, and I use an HRM. My diary is open if you wanna look around.

I eat back all of my calories. That being said I try to focus on NCB instead of TCB. I posted this thread on the topic recently:

http://www.myfitnesspal.com/topics/show/1095374-total-calorie-burn-vs-net-calorie-burn

I have been able to maintain my ideal running weight all year with this method

I too eat back all of my calories. I'm female, 30 years old, 5'7, 137-139 lbs right now, approximately 17% bf (I've was leaner but was way too hangry and gained back some fat intentionally). My BMR is est to be 1400, my TDEE est 2100 on a normal day (I'm a very busy, can't sit still type of person) and so I eat 2100 on rest days, or more on days that I have lots of errands etc and on running or workout days, I always eat back 75% of my calories burned.

I never net lower than my BMR (I have no problems further leaning out eating above it). I refuse to be a victim of my own stupidity disrespecting my long term health just to PR (I'm never going to be an elite or win races, it's a hobby), so I eat for hormone/bone health.

Speaking from the female perspective I try to maintain a healthy body fat % and avoid amenorrhea. I don't want to ever be labeled as having female athletes triad. -.- (Edited to add, that eating lots of veggies and at least 1g/lb LBM of protein helps keep me fuller on hangry running days).

I eat between 1600 and 1800 every day with the goal of losing a pound a week. I'm near the end of a marathon training cycle, so I will go up to 2000 the day prior to and the day of a long run. I run most of my miles very easy (HR ~120), so if I use the MFP calculations and eat back all my exercise calories I will gain. I don't estimate either, I weigh portions. The MFP calculations appear to assume that anyone running a 9:00 mile is working harder than I am. For reference, I'm a little guy. 5'4", 125 pounds.

My BMR is ~1500 calories; I target ~1650-1700 calories every day based on TDEE with a target to lose a little over 1 lb per week, though I'm under that more often than not. I'm one of the weird ones for whom long runs serve as an appetite suppressant, so have no issue staying at that same intake on long run days (e.g., this past Sunday, I ran 16 miles and burned >1600 calories according to my HRM... I still ate ~1700 calories that day). I may find that I'm a bit hungrier the next day,but still stick to my 1650-1700 calorie target. If I was using the MFP method (vs. TDEE) and eating back exercise calories, I just think I'd find it hard to eat all the exercise calories from a 16+ miler on long run day, and I wouldn't trust the calorie burn estimation, even from my HRM. Perhaps that's because I'm obsessively trying to drop the pounds prior to race day and am mildly insane! :laugh:

I'm one of the weird ones for whom long runs serve as an appetite suppressant, so have no issue staying at that same intake on long run days (e.g., this past Sunday, I ran 16 miles and burned >1600 calories according to my HRM... I still ate ~1700 calories that day).

I'm totally this too! Ironically I'm not hungry at all after a long run, but the next day I want to eat everything in sight! I call those my T-Rex days.

In the past year I've lost 50 pounds and rediscovered running. I'm currently training for my first half-marathon in a decade. I thought my knees couldn't handle running. It's amazing how much better my knees feel after losing 50 pounds!

When I run 6+ miles, I find that I'm really hungry. Now I realize I need to eat back these calories to fuel my runs, but I'm nervous about eating a ton of crap and falling back into my bad eating habits.

So what do you guys eat? Do you eat back ALL the calories you burn from running? I wouldn't mind dropping a couple more pounds, but it's not critical - I'm in my ideal body fat range.

You are asking the wrong question. Eating back calories is not relevant here...you eat back if you are hungry. If you are not, don't worry. The concept of eating back calories or not is more for weight loss. But you said that is not your main focus, it's just a "would be nice".

What you need to ask is 1) What is your nutritional intake before a run 2) After a run 3) And what is your hydration before, during and after a run.

Consuming slower burning carbs about 30-45 minutes before a run will allow those carbs and/or sugars present in the carbs to be turned into glycogen, which is your fuel for your run. You also want to make sure you are keeping yourself hydrated throughout the day...but be careful not to overhydrate...most people don't have to worry about overhydration though, since consuming that quantity of fluid usually is uncomfortable for most.

During your run, bring some water with you if you find you typically need it. Until your runs start getting in the 2+ hour range, your body technically shouldn't be burning through all of your sodium and glycogen stores, so stuff like Gu or Gatorade may be overkill.

Remember, hunger from running is typically caused more by lack of or poor choice of proper nutrients before your runs, as well as not staying hydrated enough.