Valve confirmed to the makers of the nvidia-PPAs for Ubuntu, what users of the current Beta-Nvidia-Driver 358.x for Linux do already know: the Beta-Driver is responsible for an unusual hight count of crashes when used within the Steam-Client. Many users reported this already also on the Steam-Client Bug-Tracker, at Reddit and also at the Nvidia Linux-Forum. Here is the official note from the Ubuntu “Graphics Drivers Team” team:

ATTENTION STEAM GAMERS:

Valve has reported lots of crashers with nvidia-358 and the steam client; we strongly recommend you use nvidia-355 until Nvidia publishes new drivers.