Seeing as I saw this linked to off of a message board, in all likelihood 98% of the civilized world has already seen this, but, for the last poor deprived 2%:

Right around the time of Matisse and all the others who pretend they don’t know how to draw, you almost might as well stop watching. But before that, watching each face fade into another heightens their differences and especially their emotions. The movements of the features as the form from one expression to another makes every thought more powerful. It’s also very eerie, because as the faces are in mid-shift, you could almost swear you see glimpses of someone you recognize. I think this feeling is most powerful right before it solidifies into new face.

I wish that it cycled through slower, but I have a feeling it’s as effective as it is precisely because it doesn’t give you time to stop and think, and your imagination has to fill in so much of it.