I did 1100 miles of the AT over the last two summers, and I did all of my food via mail drop. The advantage, of course, is that you can choose exactly the food you want (including organic, non-GMO, etc.). The huge disadvantage is that it's an enormous amount of work for you and whoever is putting together your mail drops. Drying and packing all of that food took many, many hours.
I'm doing the PCT in '09, too, and I'm planning to do just a few mail drops and mostly resupply in towns. I'll miss my homemade meals, but I can't imagine spending that much time slaving over my dehydrator.