how to check if bumblebee is working and nVidia drivers are NOT installed?

I have a laptop that supports nVidia's optimus technology. To what I gather, Linux support for it is abysmal.

I learned this AFTER installing the nVidia drivers (from Canonical).

At the moment, I've uninstalled (and purged) the nvidia drivers, followed the instructions here,

https://wiki.ubuntu.com/Bumblebee

and *think* I've got Bumblebee installed.

Any idea HOW I can check if the nvidia propitiatory drivers are NOT in my system and to see if Bumblebee is working? All I care for are the power savings (and to run the laptop cooler).