error while loading shared libraries: libQtGui.so.4 when starting Opera Mobile Emulator
Unless you are using an architecture different to the rest of your system just executing sudo apt-get install libqtgui4 should suffice.
In case that you are using another architecture just append :arch to the package name. Example, if you are using the 64-bits version then libqtgui4:amd64 is for you:
sudo apt-get install libqtgui4:amd64