Being interested in video games, I've thought a lot about rating systems. Older magazines used to use 10 (or even 100) point scales, and you quickly realize all the rating ends up taking place in the top 30-40 percent of your scale anyway... so why not limit the gradations. For my money, 5 stars makes sense... you've got a middle of the road "average" 3 star movie, and then two stars above and below.