Apparently, with my original posting here, I stepped on several people's toes. I'm sorry for that, and for this reason, I've simply removed this content (and also because - as some of you pointed out - some of the things I mentioned were not Plasma's fault, but workarounds or bugs in other areas, although to me as a user they appeared on Plasma).
On the other hand, my frustration with KDE is growing... I find my self more and more replacing KDE applications with GNOME applications, simply because the KDE application does not fulfill my needs or is buggy, while the GNOME application provides the fundamentals that I need.
(And just for the record, for most of these problems I either filed bug reports or talked to the maintainers on IRC, who told me mostly, that it's not their application to blame, but some underlying framework and I could do nothing about it...)