For anyone having trouble with the latest Unity v5.6 and Steam 1.2.1
The current beta version of Unity 5.6 breaks the normal operation of the SteamVR_UpdatePoses component (required for tracked controllers). To work around this in the meantime, you will need to manually add the SteamVR_UpdatePoses component to your main camera.
Edit: Also, the update poses script has to be changed. Replace it with the one attached. That should work. Hopefully steam vr and unity become compatible again soon with a future update. If not, there will be changes to the toolkit to accommodate the new player prefab. If there are any problems, or questions, please let me know!