KDE fail to start after clean install F14

[Armelius Cameron]

Hello,
I previously had F12. I just did a clean install of F14, but I left my /home 
intact (it's on another partition). So obviously KDE files and settings 
(~/.kde) is still the old ones. 

When I logged in, KDE would try to start but then seems to die. X would just 
quit and give me back KDM. I can't tell what's wrong from looking at Xorg.log 
(it just say X exit unexpetedly or something like that). 

I tried removing ~/.kde so it would start fresh, and that works. Obviously 
that works as a backup plan: just start fresh and reconfigure all my KDE apps 
again. But if possible I want to avoid that. Any idea where I should start 
looking why things go bad ? Does KDE has its own log ?

Thanks
AC