I was rather anxious to use KDE 4.
Many applications lack the features of it's KDE 3 counter part.
I gave it a try 3 days ago and didn't end up reinstalling it
It can be considered a great success.
P.S. I ended up uninstalling all KDE 3 apps and leaving only KDE 4.
P.S.2 If You want Your KDE 4 fly don't use Compiz with it.