I installed KDE 4.11.0 from the backports last week and am for the most part happy with it. However I did notice a couple of things. The screensaver locks from time to time but the computer is not but I still have to do a hard restart. The simple screen locker works fine so this isn't really an issue for me and the startup and log off sounds no longer work. This too is not an issue but was wondering if others have noticed the same thing.
I did the upgrade on 3 different machines with the same results so I don't think it's a machine issue..