The contrast slider does something for sure, but it’s effect not very strong – you’ll see it on certain color schemes very clearly, less so on others. Some other issues might be due to X.org configuration (does compiz work?) or the packages you use. I think once distro’s start shipping KDE 4.0.1 or 4.0.2 the worst bugs will be fixed, and things will be a bit more smooth.

In my short (1/2 hour) playing around I found the following bugs:

* Often the desktop icons’ hover effect (the thing that lets you rotate them) stays on even after you move the mouse off them.
* Somehow (I think I was trying to move an icon) I moved the desktop background! Seriously! After logging in again I had no background and couldn’t get one back by changing it in the desktop settings.
* Speaking of that, the current background drop-down in the desktop settings isn’t initialised correctly.
* Couldn’t get any of the fancy KWin effects to work at all. They never complained, just nothing happens. Using the nvidia driver.
* Changing mouse cursor theme doesn’t work without restarting X.
* Changing the oxygen contrast slider doesn’t do anything.
* Files still open with Konqueror by default (I thought it was supposed to be dolphin now?)
* Just before windows appear they often start as either a black rectangle, or one that looks like uninitialised memory.
* The ‘Add Widgets’ button in the top right desktop corner thing looks like it is supposed to slide in from outside the screen. Actually it pops up and then slides a bit.
* KRunner doesn’t start in the middle of the screen.
* You can’t resize Kickoff, or configure the panel at all really.
* Everything is pretty slow.
* Probably other things I can’t remember.

Just sayin’ … KDE4 doesn’t rock *that* much (so far). Still, well done to everyone involved!