I only tie leaders myself these days for special occassions - and for that, there are of course a number of good reasons. I'll get back to that.
Several years on, and factory made, tapered leaders are now very good and there are numerous specialty leaders on the market. They aren't better than the ones you can make your self, but one major advantage is that you get rid of the bulky knots in the heavier parts of the leader. 15 years I tied 4-6 foot tapered leaders for sinking lines, which you couldn't get back then, and now, I know that both RIO and Scientific Anglers make them (and maybe more).
Especially during the summer it's nice to be rid of the bulky knots as they tennd to catch weeds.
I have spend some time designing leaders that fit my wishes by using shor(er) tapered leaders and building on them. That can work really well if you're willing to spend some time with a caliper, sacrificing some leaders and spend some time testing them. Oh, and by the way - if you like long fluorocarbon leaders, you'll be forced into that now. I've just heard that 12' flurocarbon leaders are no longer made - anywhere. It's of little consequence to me as I don't like fluorocarbon that much. I use it on heavy sinkers for the DH rods because it's more resistant to abrasion than nylon, but in general, I much prefer nylon. I find it casts better, and most importantly, fluorocarbon has a millennia-long degredation rate and nylon disappears much faster if you loose a piece on a snag.
For most of my dry fly fishing, I still use hand tied leaders almost all the time. The reason being that most of the water I fish are quite small, and a 15' or even a 20' leader make no sense at all - certainly not when combining it with the almost always present wind in the streams I fish. So I resort to a shorter leader - sometimes only 10' in length, and in order to get a leader that perform well for drag free drifts, I tie my own. Basically, this means I make leaders with very short butt sections to give them a mediocre turnover, which makes different slackline presentations much easier under difficult conditions. It's a compromise, of course, because I also want to be able to present a fly into the wind. And the bulky knots? Well, I'd rather be without them, but in this case, I'll have to stick with them (at least until Sa or RIO gets on the horn and buys all my leader designs and sell them by the billions, so I can take over the World).
All the years spent tying leaders and experimenting taught me lot, and most importantly that the leader is an incredibly important part of the cast (so important, in fact, that in the olden days in the UK, the leaders was simply called "a cast" :-). Often its importance is overlooked, which is a shame, because it's very interesting to experiment with and at least as much fun as trying lines and rods.
If you haven't - do try!
Have a great weekend,