Optimus is not perfect yet. Notebookcheck and other review keep mentioning that Geforce will be occasionally triggered even we have no intention for it to run.

Flash is one of the culprit. Even the flash ads will sometime trigger optimus. Basically, I just change the optimus setting from Auto to CPU. HD3000 is fast enough to handle flash or even youtube at full hd.

Switch back to Auto or GPU if you want to play game.