It pains me to say this, but from my own personal experience(s)...the fault most often falls upon the fisherman.
When first experimenting with Braid many many moons ago...I quickly learned that I was going to have to reteach myself in the way I retrieved my line. That applies to all types of fishing and retrieving methods REGARDLESS of lure and regardless of how I wanted to present that lure to the fish.
In regards to the "too much focus" comment made earlier, YES..it will require focus, but that goes away once you've permanently adjusted your retrieve techniques when fishing braid. It becomes second nature. If someone has honestly given it their best shot and continues to have issues, braid just may NOT be for them.
(*Rule #1 - which has been posted many times before in this and other threads, you CANNOT over-fill your spool. Everyone has their own idea of what "over-fill" is though..so this too will vary).
This past season I was fishing side-by-side with another angler. We were both fishing braid, coincidentally the same mfg, denier and color. However, the other angler was continuously getting bird-nested. He was complaining out loud in what appeared to be a call of help. As I slowly moved in his direction he began asking questions. He too had noted that I was using braid and was not having any issues. We discussed the possibility that it could be our gear as they appeared to be on different sides of the tackle spectrum. While I did not rule that out, I tried explaining how I felt that the method of "retrieve" was THEE most important aspect of fishing with braid (2nd to overspooling). He was faulting the reel as being the problem. In my attempt at helping this gentleman, he asked if he could attach my reel to his rod. I obliged and let him have at it...within a few casts, my reel was a ball of junk...I quickly grabbed his set-up and was able to save it (I have a love for undoing knots, for some reason God gave me patience for it...not so much in other avenues of life, but for knots, yes...go figure!)
Ok, so now he's starting to think it's his rod...we then attach his reel to my rod and he has at it.....
.
Eventually all gear is back where it belongs and I simply suggest that we switch entire set-ups and give that a shot for awhile. Needless to say, I never got a wind-knot nor a birds-nest while using his rod. On the other hand, I was going to have to respool my rod when I got back home because I wasn't able to correct all the issues created while he was using it.
This proved to ME, that aside from over-filling your reel, your method of retrieve falls into 2nd place when experiencing birds-nests along with most wind-knots. Constant pressure needs to be applied when retrieving braided line. I'm not suggesting squeezing the line between your fingers pressure, but some pressure needs to be applied. It's not rocket-science, but it does require
some. Depending on wind speed and direction, sometimes a finger squeeze is necessary when retrieving that large bow created by the strong wind when it took it a mile to the left or right....sometimes you can't just simply "pick up that slack", you have to pinch it. At least that's what I've learned through my own personal experiences.
Here goes a self-ginx for 2013, but I have NOT had a braided-birdsnest in many years, even wind-knots are very FAR AND FEW for me....I better brushen up on my knot-breaking abilities now..
