Another two things I noticed:
Selecting text with the mouse...
....in the message window: quite fast/no lagging, nothing special about it
....in the editor window: slow/lagging, some noise comes out of my PC. I tested the HDD with wmhdplop -> It is not the HDD making the noise. What is it then? Maybe the graphics card, because it is the same noise I sometimes hear while using 3D applications...
You see the difference? The editor is really doing something stupid here!