Update.
A few days ago Mint Linux KDE came out. It is based on Ubuntu 12.04. But they took Gnome version of Mint linux as system to base it on, not Kubuntu.
I have abandoned KDE during the famous 4.0 dabacle. Before that KDE was my environment of choice. I have decided to try going back to KDE to see how Mint developers have configured it. To me it is much better than Kubuntu or other pure-KDE distros. I dislike Plasma and the typical modern look of KDE 4.xy
So I have installed Mint Linux Maya KDE edition, (googled how to disable that *bloody* Plasma cashew icon on my desktop

,) tweaked system a little bit and started to use it. It even has wobly windows and desktop cube! This is Mint I have come to expect. Everything works very well, even on this 8 years old Pentimum 4 [Hyperthreading] based PC with 2 gigs of Ram and old disks.
I haven't had single crash since converting to KDE. I have spent quite a few hours using Calibre very intensively and everything Just Works (TM).
UPDATE more than a month later:
I still haven't experienced single crash of Calibre or any other program since turning to KDE.