Exactly the same issue on Asus N550JV laptop (hybrid graphics: Intel HD 4600/nVIDIA GT 750M), fresh install of 14.04, nvidia-331. Random lockups when using nVIDIA card, no lockups at all when using Intel. Lockups happen more often when nVIDIA card is under load (for example, playing Civilization V).
Exactly the same issue on Asus N550JV laptop (hybrid graphics: Intel HD 4600/nVIDIA GT 750M), fresh install of 14.04, nvidia-331. Random lockups when using nVIDIA card, no lockups at all when using Intel. Lockups happen more often when nVIDIA card is under load (for example, playing Civilization V).