Comment 8 for bug 1007423

IBus in 12.04 and earlier versions lacks a dependency to "gnome-icon-theme", you may need to install it manually for Kubuntu.
sudo apt-get install gnome-icon-theme

im-switch should be the recommended way of enabling IBus, instead of manually change environmental variables.

Built-in Firefox should work. Changes are that you download Firefox from Mozilla which is 32bit. 32bit Firefox don't work automatically on a 64bit system because of some technical reasons.

LibreOffice works on my Kubuntu 12.04 64bit box currently.

Other random apps should be discussed case-by-case.