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Yup, my point exactly.
In an "ideal world" all the users trying KDE4 would have enough knowledge and patience to identify the exact cause of the problem (and perhaps fix it - that's often equivalent to identifying the culprit), go to a valid bug tracker and never ever mention in public that KDE is running slow or is unstable (even if that's exactly what they experience).
But in the real life the users will spend 1~2 hours on "trying new KDE4", hit an issue they can't resolve themselves, and spread the word to anyone daring to ask about how KDE4 is slow and unstable.
But, is it fair? Well, IMHO it's not fair that KDE4 gets all the blame. But they do deserve bad publicity. After all it is their product that wasn't robust enough and their poor design and testing practices that produced to it.
Besides, who cares?, Ultimately, the goal is to make a better DE satisfying needs of more and more users and not to cover problems with excuses.