so i finally upgraded that machine that was running a 6 years old duo-core to a newer i3. i decided to give Mint 14 KDE a spin this morning. everything worked as expected, which is usual from the Mint team. one thing i like about KDE is the eye-candy factor. it's easy to add widgets on the desktop and such. on the downside; fonts look ugly in Firefox unless you go in the System Settings and tweak the fonts properties. Dolphin still does not remember folder thumbnails. if you haven't used Dolphin for a few minutes, it takes 4 seconds to launch. the same time it took on my 6 years old machine. it those little inattention to details that just drives me nuts. i'm gonna try XFCE 14 next. i quite enjoyed version 13. theming the windows and desktop looks much better in a Gtk/XFCE environment than in a KDE environment, imo.
so i've done a little bit of research and it would seem the slow start of Dolphin is due to it to connecting to a DNS. nepomuk integration, most likely. i'll have a look tomorrow when i'm back from work and try to tweak Nepomuk and Dolphin to see if disabling Nepomuk in Dolphin makes any difference) anyway, this should not be enabled by default or at least tweaked. other file managers like Nemo, Nautilus, Thunar etc don't have this issue. and there are still no solutions for Dolphin forgetting folder thumbnails, months after i went to the KDE forums for help. the devil is in the details.