Ubuntu uses GTK+, i.e. the Gnome environment while Kubuntu uses Qt3 or Qt4 for
the KDE environment - different window managers.

I you are using Gnome, unless you have loaded the kde-desktop package in order
to compile a KDE application that does not exist in Gnome, e.g. Tork, a Tor
controller similar, but better IMO to Vidalia, then you probably don't need any
KDE libraries.

On the other hand, if you have installed some packages that required KDE
libraries and have since been upgraded, and you decide to check as has been
advised, you don't need to write anything down. Just issue the following
commands:
1) cd /var/lib/dpkg/info
2) ls -1t *.list > ~ubuntu/Desktop/pkg.lists
This saves all of the packages you have installed in the Desktop file,
pkg.lists.