Comment 26 for bug 1061073

i see the same behavior (slowness, artifacts). moreover, when using "kwin_gles" instead of "kwin" the screen does not seem to be re-drawn correctly. for example, invoking the "run command interface" starts to show it but does not finish the animation. the result is that you type but don't see what you type.
finally, turning off "use opengl 2 shaders" in the effects-config doesn't change anything either (neither for "kwin_gles" nor "kwin").

i hope this helps in some way to narrow down the issue.