Being a Plugin developer myself, each and every review and rating I receive encourages me further to improve upon my plugins. Unfortunately very few happy people take the time to write a review.

I recently had a guy who happens to be a user of my Wp-Insert plugin for the past 4 years or so on over 3 dozen sites who had given the plugin a 5 star rating and a good review. The plugin did not go well with one of his new installation and he rewrote the review and opened up a support comment thread saying "Comment Changed-Stars Reduced to One" and emailed me that he will revert the stars If I fix the issues for him! He kind of wanted to hold me hostage with that review.

Some people do misuse the review and rating system and there is nothing we can do to fix it. Such mischiefs can be reduced if lots of people begins to leave review letting law of averages take over...

Kudos to the initiative.