Since KDE is probably the most common window manager (if not the most common, then at least the second most common <grin>), it should get these three issues right:
1. very slow to refresh file list when you go to a folder with lots of files - windows is much faster
2. when you move lots of files using Konqueror, it takes forever to move them, whereas "mv ..." would do it almost instantaneously. Poor!
3. Every now and then I have to re-associate files with the right programs. XLS will open with gnumeric for a couple of weeks, and then suddenly start opening with OpenOffice. Same thing with AVI being opened by mplayer, then after a while it tries to use XMovie. Sigh.