I've definitely seen a slight drop in reviews, which is a shame but it can vary from video to video.
As for their usefulness - I think there are pros and cons.
pros:
- people are actually more honest when they know you can't find out who is giving the score - it's a good indication of how much someone liked something. I can see more people giving 1s and 2s in the star scale who wouldnt have in the regular review system for fear of what somone would think.
- the ease allows people to give a small opinion of something that they would find it hard to write a full review on
cons:
- less full reviews
- no reasoning behind the score - is it based on entertainment, quality, song choice... what?
- no advice on how something could be improved
That last one is a big problem, I think. In my early days as a creator, good advice was essential in me getting better at making videos. Nowadays it seems that people only want to leave opinions on really good videos, which invariably don't need much criticism. Review swaps are pretty much the only way to go now... I see no value in star swaps.
I think there already is a difference between the star rankings and top 10% - mainly because of the way the top10% is calculated. In the top 10%, 1/3rd of the overall mark is made with the Reviewable score.
For this reason, despite having very high scores in all other categories, Arima Shinjikun didn't make the top 10% for a long time because the video isn't very reviewable. It's doing well in the star scale, though. Shameless Rock Video is doing better in the star scale for similar reasons.
I haven't totally made my mind up about whether the star system is good or not. There is another problem that it favours new videos because you can only review ones you have recently downloaded - ones you have already dont get much of a look in. Where's tainted donuts and failed experiments? - not on the carrot so not on the star system. That definitely needs to be fixed
