I found very useful installing several desktop environments but creating separated accounts to use them. I have installed Ubuntu 12.04.
- I have the default Ubuntu 12.04 Unity Desktop under the default user account "mauricio". This account is my Unity Desktop. But then I wanted to have a GnomeShell desktop and,
- I installed Gnome-Shell and created a new user account with name "VenGshell" and I use Gnome-shell there and configure the whole account with Gnome-shell. So my Unity preferences in my Unity desktop have nothing to do in this Gnome-Shell account, Get it?
- Then I wanted to have a KDE desktop in this same Ubuntu installation. So I installed the Kubuntu-Desktop and created another user account under the name of "MaVriK". And I configure it to use KDE desktop environment and, of course again, It is completely apart and nothing to do with the other desktop customizations.
This kind of configuration is, IMHO, the best way to have every desktop environment living together under the same Linux installation.
- If I want to use Unity: I login under "mauricio".
- If I want to use Gnome-Shell: I login to "VenGShell".
- If I want to use KDE: I login to "MavriK"
I never ever have any performance issues under this configuration, in any desktop environment.
About applications all showing in the Apps menu? I just do not really care about it! because for that task there are the panels. I have access to my prefered apps I use to use daily in those panels, I just add the app icons there and forget about app menus.
And if I want to launch an app in particular, there is Gnome-Do to easily "DO" that task!