Here is a solution that I have found mitigate display/window decoration issues when switching between KDE and Xfce.
How do I find which files KDE has modified?
Finding the files that have changed in a home directory, within a specified time period, is fairly straightforward.
find ~ -maxdepth 5 -mmin 10 (searches for changes within the last 10 minutes)
However, the results are cluttered with a large number of dynamic files(various app caches, for example). So, I needed to exclude those from my results:
find ~/ -maxdepth 5 \( -path ~/.cache -o -path ~/.xchat2 -o -path ~/.local -o -path ~/Downloads -o -path ~/.config/deluge -o -path ~/.config/chromium -o -path ~/docs -o -path ~/.dropbox -o -path ~/Dropbox -o -path ~/.pulse -o -path ~/.dbus \) -prune -o -mmin -5
This results in a much more manageable list to identify the files KDE has modified(I don't doubt that there is a more elegant solution to get the same results).
What files need to be changed and what commands should be run?
Prior to exiting KDE, enter a terminal(Ctrl-Alt-t), and enter the following command:
rm ~/.gtkrc-2.0
This will remove KDE window decoration settings and its deletion will result in those settings not being applied to Xfce. However, once logged into Xfce, the WM will need to be reset with the following command:
xfwm4 --replace
Additionally, if any theme or font changes have been made while working in KDE, another file will need to be deleted prior to logging into Xfce. Otherwise, fonts in the web browser will have been modified.
Again, from the command line:
rm ~/.fonts.conf
How can I (partially) automate this?
I have automated part of this by editing /etc/lightdm/lightdm.conf and placing the following lines in the file:
[SeatDefaults]
session-cleanup-script = home/<userdir>/clean_up_after_kde.sh
The script contains the two rm commands from above. The xfwm --replace cannot run until the desktop environment has already started, so this is still run manually.
In order for the changes to take effect, lightdm needs to be restarted. Run the following:
sudo restart lightdm.
Your session will immediately restart after this command and drop you back to a login screen, so ensure that you have saved any work before restarting.
These commands will be run as part of the logout process now. Note that this script runs only after the user is completely logged out.
While this is still pretty kludgey, it is a smaller step to making it less so.
Best Answer
Xubuntu
You may also want to have a look at Xubuntu that comes with the lightweight Xfce desktop. This also includes a customizable launcher (here shown at the bottom) that can also be moved to the left side like in Unity: