The one leader I still tie myself is my dryfly leader. I touched on that last weekend too. The reason is that "my" dry fly streams are quite small, and a very long leader is rarely desirable. In dry fly terms, I'd say that i use quite a short leader in many cases.
Very early in my fly fishing career, I met a guy, John Petermann, who taught me so much and gave me a serious kickstart, and he was also the first to point out to me the importance of leader design. I met John because I had started tying dry flies and had trouble keeping them on the surface. The main reason was lack of tying skills and crappy materials. I went into the store John worked in then, because I had heard he knew a thing or two about dry flies. Instead of trying to sell me a genetic cape, John simply invited me home that same evening to teach me how to tie parachutes, where hackle quality means less. That turned into a long friendship.
But back to the leaders - and to John, because the dry fly leader I use the most is based on John's design. John published his leader design years ago in a chapter in a Danish book on grayling flies (cover shot in the PoD - don't bother looking for it - it was, unfortuntely, a small, private edition in only 200 copies). Here's John's recipe (metric and in diameters:
This gives you a leader around 4-4,5m in length.
I use this same recipe still, but I very rarely make my leaders over 4m long for fishing in Denmark - I will on occassion, but I try to keep them around 4m. The "seceret" in this leader is in the lengthening of the sections from 0235mm and down. This allows the leader to slightly collapse, which aloows for better frag free drifts.
One great advantage of these "self tied leaders" is that it's very easy to make adjustments. If for instance I was to present a large mayfly into the wind, it's easy to length the second-last section and shorten the tippet a little - you'll be amazed at the difference even a slight adjustment can cause. And on the other hand, I can also shorten the tippet section down to say 30cm, and add an even longer, thinner tippet for fine presentations of small flies.
This versatility - and the fact that it's impossible to buy a factory made leader designed to collapse, is why I still tie my own dry fly leaders.
Scientific Anglers old 7'6" tapered leader was a close enough replacement for the above knotted butt section, and I used that for a while, but I'm not sure how the tapers are these days, since they don't show a taper profile on the leaders anymore. I feel a leader-measuring-session coming up as soon as I get my hands on a proper caliper. I really is nice to be rid of the big knots in the heavy parts of the leader.
Have a great weekend!