QA Team and a Extra Mile Initiative and I would say that they are doing pretty good job nowadays. There hasn't been major bugs that would have affected me in 4.x.0 in a long time and even the first betas are usually working fine but if that isn't enough KDE releases five bug fix releases for every major version.
I think there's something seriously wrong with your distribution if Plasma, Amarok and Nepomuk are crashing or "exploding". I remember Nepomuk crashing in some beta year or two back, Plasma used to crash in the 4.3 times but after that and Amarok has never crashed for me, I think. I'm sure you have reported those bugs for your distribution/KDE?