Version:            (using KDE 4.2.2)
OS:                Linux
Installed from:    Unspecified Linux

Moving an icon on a folderview, with kwin desktop effects on, is very cpu intensive. Moving 4-5 icons makes kwin slow down and freeze until the compositing check makes kwin disable composite.
Moving icons shouldn't be such a difficult task to do and indeed it is not when using compiz for desktop effects. With it icons move smoothly and cpu usage stays low.
This bug seems somehow related to another issue:
when selecting text in firefox 3.0 and dragging it, we get the same slowdown and freeze until kwin composite check disables desktop effects. Again everything is smooth with desktop effects off or using compiz for destop effects.

I've seen this in 3 different computers, using intel (945gm and 965, with both exa and uxa, kernel 2.6.28/2.6.29/2.6.30-rc2) and ati cards (free radeon driver, same kernel versions).

So this doesn't seem like a driver issue (different cards and driver versions, compiz works), but more a kwin one