I've noticed that with the latest versions of KDE, the screensaver Kcomten 4 and the Bespin style theme not properly work. It is disappointing that the best screensaver and the best style theme, lost and cease to exist.
If KDE is that way, over time, it will become a common and equal to the other DE. KDE needs more eye candy, no more simplicity.

re: Kcomet4
-1st I must say that that is a pretty cool screensaver and seems to work fine for me
-2nd it seems to work fine for me so I would suggest you make sure that it was properly updated to the proper release by re-installing it and then retry and also test as a new user

re: Bespin
- as i don't use it i'd suggest you try the same as suggested for Kcomet4

Sorry, but that is false: Kcometen4 not take a screenshot for the cube effect, use image identification. If you give test shows how all is well, but if you give them apply what happens I'm telling.
when trying to install bespin, the system proposes uninstall: kde-window-manager, kubuntu-full, kubuntu-netbook, kubuntu-desktop, plasma-widget-toogle-compositing, and proposes install: kdewindow-manager-active, libkwinactiveeffects1abi4, libkwinactiveglesutils1, libkwinactiveglesutils1abi3
Do you think that all is well?

re: Kcometn4, made it my screensaver and the comets work fine and the cube seems to also (I used an image file) - maybe I'm missing something but for me seems fine. Try renaming the rc file in $KDEHOME/share/config

re: Bespin, gonna guess your packages or repositories are messed up from your KDE upgrade, would suggest you do a an apt-get upgrade - note: this is a distro issue not a KDE one

also make sure all your ppa's are correct