If you’re running KDE 4.5.0 beta 2 from the Kubuntu PPA and are wondering why your widgets disappear every time you login, it’s because beta 2 has a bug where it gets really confused about which activity you are using – use meta-tab (windows-tab) to switch between them and you should eventually find what you’re looking for..

Also if you’re wondering why the “Printer Settings” option isn’t working any more and giving a strange error message, it’s because it’s now looking for a Python module which isn’t packaged in Ubuntu (kubuntu-ppa bug 591980), it’s complaining that:

systemsettings(22750)/python (plugin): Failed to import module
 Traceback (most recent call last):
   File "/usr/share/kde4/apps/system-config-printer-kde/system-config-printer-kde.py", line 64, in 
     import cupsutils.ppds
 ImportError: No module named cupsutils.ppds
 systemsettings(22750)/python (plugin): Failed to import module

In Debian the module it’s looking for is in the “python-cupsutils” package, but that’s not in Ubuntu.