Although a nail knot is the cleanest, best-performing connection between fly line and leader, I hate tying them, so I usually use the nylon braided loops that come with sink tips (or sold separately). The loops do create a "hinge" in the system that can compromise a bit of casting potential, but for the most part, if you keep your casting loops tight, the loops won't kill you. Plus, they make changing between different types of leaders (sink tips, mono, furled, etc.) a snap while in the field. I know a lot of folks don't like them, but I do. Just make sure you use super glue on the loop to line connection.

Another thing I have tried, with some success, is nail-knotting a short butt section to the end of the fly line and tying a perfection loop at the end of the butt section (D3 mentioned the loop system). This keeps you fishing for a long time without retying the nail knot, but I find it doesn't cast quite as nice as a straight knotted setup, and I sometimes have trouble with the leader getting caught on the tag end from the perfection loop while the cast is unrolling. That can lead to some nasty tangles if not identified and addressed immediately.

I will say that D3's setup sounds like a good way to split the difference, so to speak. With his system, you will only need to tie a new nail knot occassionally (when your butt section gets too short or too worn), and you will retain the integrity of the system, which will make you a happier caster. If not for the fact that I know it would mean tying more nail knots over time, I might give it a try. Heck, maybe I'll give it a try anyway....