Thinkpad W520 with Quadro 1000m, optimus disabled.
Reading a little bit about the topic, I thought I was well prepared and did the following:
sudo apt-get remove --purge nvidia* sudo add-apt-repository ppa:xorg-edgers/ppa sudo apt-get update sudo apt-get install nvidia-331 sudo apt-get --purge remove bumblebee sudo reboot
Alas, despite the bumblebee precaution, next boot takes me to X-mode. I purged the nvidia and after reboot I was back in Unity mode. Is the official driver from nvidia a better idea?