Waited a couple versions or so, can confirm issue is now gone in 376.33. Tested on a Dell XPS 15 with a 960M.
This issue seems to be only on the M - MX family. Desktop GPUs aren't affected.
Due to the influx of the "Blender is lagging" posts, I'm going to pin this on the main site until the issue is resolved, and our close-votes review queue calms down. From what I've seen only 2.78 users are posting but it might affect other versions as well.
See Blender 2.78 with Windows 10 lags when interacting with the UI and the official release thread for the driver is here https://forums.geforce.com/default/topic/978895/geforce-drivers/official-376-09-game-ready-whql-display-driver-feedback-thread-released-11-28-16-/1/
DO NOT UPDATE TO Official 376.09 Game Ready WHQL Display Driver (Released 11/28/16).
If you have already, the best "fix" is to rollback to your previous working driver, personally 375.95 seems to be a good version in the same month. If for some reason you can't do this, open the NVIDIA control panel and force Blender to use the intel chipset, if you have that option (not recommended as you might see flickering).