My experience is there is a fairly big delay in reviews showing up - but I would expect even the first review to get published within a month of posting should other ratings and reviews arrive for that app to separate it from an app that has less than 100 downloads ever.
I don't know for sure, but the ratings seem to be held back until 10 or 20 are submitted. Once you reach that limit the store will show the overall rating and only new versions get ratings once they hit their threshold (but a message stating not enough ratings are in to show).
It makes sense for users to expect a few points before any app gets zero or five stars and makes the ratings a useful measure that some handful of people expressed an opinion before they are shown.
After hearing about the delays, I've sometimes checked and my experience with about 50 reviews where I cared to check back, the shortest time was about 24 hours and the longest was 2 weeks for a review to appear. I've not had one not eventually get published, but I also don't generally review apps that have hundreds of reviews which is much harder to find your needle in the haystack of other reviews. I generally star those apps or write something and not bother to check if it ever made it live.