Today I updated my Arch. I wanted to give a try to Nouveau driver, because nvidia blobs drives me nuts (it works veeeeery slow and choppy when it comes to resizing windows).
So I installed nouveau from repository, restarted everything. I expected that desktop composition would not work as always or I get artifacts, I haven't read on internet that it would work (I found many posts saying that for now it dont' work). But to my surprise, when I logged to my box I saw that KDE4 turned on compsiton (OpenGL mode) by default (!!!) and it worked very fast an resizing windows was very fast and fluent!