My suggestion is to not have a percentage rating but instead have it like Amazon user reviews - you vote whether you found it useful. Then the statistic is just those who voted yes or no and in the end, you show the number of people who did e.g. 4 out of 7 users found this review useful. This means 4 voted yes and 3 voted no.
I dont think its necessary to have a user percentage rating as well as the individual reviews should be the key, not the reviewer.
I agree with being able to change your vote if the review changes.
Edit: I also agree with having the number of views/votes/comments shown on your profile so you can quickly see the community reaction to your reviews.







