Could it be that the system gets slow after mounting an external share which is switched off? What I mean is this:
when I mount a shared disc in my wife's computer I can use it as if it is locally mounted. Then suddenly, when she switches of her PC, Dolphin comes to a halt. It takes like forever before I see some icons on my screen in Dolphin and the only thing to do is reboot.
Is that the same experience as you have?
No more Windows and Gates since Ubuntu 8.04, used 9.04 and 10.04 then switched to Kubuntu because of Unity and Gnome 3.
After that it is Mint, used 9 till 15 all in KDE version and loving it.