I just installed Xenial, and I attempted to install the proprietary NVidia drivers. However, when I rebooted, the system went to a black screen (not even the backlight was on) and I had to reinstall. This happens with all three of the available choices of drivers (304, 304 updates, 340).
I'm using a MacBook Pro 7,1 with a GeForce 320m inside. The Nouveau drivers eventually crash the machine after about six hours of uptime and aren't good while they're running anyway.