Some good info in this thread, but so far nobody has mentioned this. Carry a few replacement blades and you won't have to worry about dull. I never field sharpen a knife any more.
When I found out about Havalon knives, I told all my doctor friends who hunt, and my taxidermist friends. I found out they all use them, although not all of them knew about the folding mechanism the blade attaches to. They were using them on a fixed handle.
I figure if it's sharp enough for doctors, it's sharp enough for me. Saves a lot of time and weight. Wish I would have had one on my moose hunt.
Steve.