Hey there, I wanted to post again after doing some detective work. First of all, from what I found out formulas using age and precentages can easily be skewed if you are pretty fit. Resting heart rate can mislead, too. I talked with a trusted trainer at my gym and she suggested using formulas as a guide, but paying attention to how you feel at certain heart rates as well as how long it takes your heart rate to recover to figure what zone you are in at certain heart rates(a metabolic test is most accurate, but they do cost money).
Using a formula that accounts for fitness level and looking for physical signs of exertion put my anaerobic threshold at about 185-190, and my max fat zone between 150-175. When you reach your anaerobic threshhold you should be breathing completely through your mouth, very mentally focused, only able to say a few words, and not able to sustain the activity for more than several minutes (as in an Imax blast). In the max fat burning zone you should feel as if you could go on for quite awhile and say some sentences. I recover from 190 down to 150 in about thirty seconds, which the trainer said was good. My resting heart rate is about 60 last time I checked, but it's easy to mess that up if you haven't been still long enough.
This was long, I know, but hopefully it helped. I know I've been frustrated in the past by formulas not fitting me, so I know how you feel.
Kelly