People seem to understand stars roughly as well as thumbs up / down (except for some people who review "best ever. 1 star." which does happen). But if you drop

People seem to understand stars roughly as well as thumbs up / down (except for some people who review "best ever. 1 star." which does happen). But if you drop it to up/down you lose any signal in the 3-5 stars range, which make up a ton of review rankings.