Is there a way to reset kubuntu to the initial state? Under initial state, I mean the system and all settings are as kubuntu was installed on a clean disk, but to preserve installed packages.
If possible I would like to avoid making data backup and reinstalling kubuntu.
If the idea is to return KDE to the default state, if you rename your ~/.kde folder (hidden) to something like kde-bak, then when you log back in you'll see the desktop as it was when you first installed. That will do away with some configurations that you might miss though, like for your kmail e-mail account (including e-mails), but in that case you can copy the ~/.kde/share/apps/kmail back from the renamed (kde-bak) folder. You won't be able to rename the .kde directory while it's in use, because it will re-create itself, so the best way to do it is from the Recovery Mode or from a Live CD environment.