All of it. The simple fact is that software projects are nontrivial; we build our own domain knowledge, really, directly into our solutions. Domain knowledge transfer is costly, both for the transferrer and for the transferee; this has not changed. And I, for one, believe it never will, no matter what the practices and tools used. Things may get marginally better, but the simple fact is that teaching and learning are both expensive and difficult things, and there's just no way to avoid them.
