Just wait until eye/face-tracking becomes a pervasive thing in VR/AR.<p>It's not just "hey, we saw that you were looking at this a lot, so you must be interested".<p>It's also, "User #8187489923323 has recently and consistently expressed slight disappointment when looking at their reflection in the mornings - the next time this happens, play an ad for the latest antidepressant tailored to their demographic with their favorite song in the background"