Being relatively new to the whole mountain biking thing (< 1 year) I still have a lot to learn, but I try to learn fast.
Sunday I was out at Lake Sherando in Virginia. These were by far the hardest trails I have ever been on. Steep switchbacks had me pushing my bike for 45 minutes or so. Boulder fields made me want to give up biking all together. When we finally got to the fun part - a fifteen to twenty minute descent I was back on board whole-heartedly. I was flying and felt in control. I had more air time than I have ever had - lots of small drops at high speed. The only problem I had was when I tried to brake before a drop. No flying, just awkward drops, nose down.
The lesson- braking causes momentum to move forward causing the fork to dive and makes lifting the front end very difficult. This is the case whether using the front or rear brake. Think ahead. Brake ahead of time if you want to slow down, but let go before you hit that drop so you can return your center of mass rearward for smooth air, and a safer landing.