If you're an idiot like me and do this:
sudo apt-get --purge remove nvidia-*
You'll soon realise your display looks a little crappy, because you've turned off your graphics card drivers. Not to worry! You restore like this:
sudp apt-get install nvidia-*
then go into /etc/modprobe.d/blacklist.conf and remove any 'blacklists' to nvidia drivers, then restart the x-server using
sudo /etc/init.d/gdm restart
Normal service resumed, and you are free to make a new balls-up!