I have been trying to use KDE 4.11 twice. My first attempt was 4.11 RC1 and it failed miserably since KWin keep crashing on my desktop so i had to postponed of testing it further. My second attempt was 4.11 Final and again, it failed due to the same reason. After that i gave up and downgraded to KDE 4.10.5 which was rock solid and stable.
I discussed this matter with Walecha and some other Slackware user in AlienBOB's blog post about KDE 4.11 and we thought that it might be Qt who need to be upgraded to 4.8.5 so that it should work fine. So i pulled Qt 4.8.5 and adjust Slackware's Qt SlackBuild (since there are two patches that are already part of Qt 4.8.5, so no longer needed) and build the package by myself.
After upgrading Qt, i continue by upgrading to KDE 4.11 and reboot my system. I logged in to my desktop and surprisingly, no more crashes here. It's still less than 24 hours, but i hope this will work in the future as well.
So, for those who wanted to try KDE 4.11 and having a crashed KWin all the time, please try to build Qt 4.8.5 and upgrade it before installing KDE 4.11. Don't forget to make a backup copy of your .kde directory under your home directory just to be safe. You can delete it later when you have make sure that KDE 4.11 is working on your system.
After this, i will need to rebuild digiKam since KDE libraries has changed, but i will not rebuild amarok as Eric has stated that amaroK 2.8 will be pushed to -Current on the next batch of update. I can live with 2.7 for few days.