[chrischen]

You still have to be careful with a +/- rating system, because for it to work you need a constant number of viewers for every item. The more the actual number of viewers deviates from the ideal constant then the more unfair the voting is. An example would be a popular item getting more finite votes because a larger sample of people were exposed to it. So a +/- system probably must be expressed as a percentage to correct this problem. However I can see a 5 star system being improved by showing some sort of relative data too.

So I guess a +/- system may not necessarily be more advantageous. It all depends on how carefully and correctly you interpret the data.