Rating systems are fundamentally flawed for many reasons. This article explains one of them: http://gigaom.com/2011/07/13/recommenda ... -research/
Another issue with rating trails is the diversity of riding styles. One person might love a slow, tight, technical trail, while another person hates it and would prefer a fast and smoother flowing trail.
Trails also change with time and weather, so a rating recorded now for a trail from a particular user might be a complete misrepresentation of their opinion of the same trail two years from now on a dry summer day.
Maybe a more useful feature would be to allow users to "tag" trails with key words ("smooth", "tight", "flowing", "sandy", "hilly", "flat", etc). That would both allow people to get a decent idea of what the trail is like by viewing the tags for each trail and make their own decision of whether they think it might be a good trail to ride, rather than relying on an average of other people's personal opinions expressed as a rating on a scale of 1-5. I could also allow trails to be searched/filtered by keyword tags.
Even this keyword tagging isn't perfect though. People have different personal opinions on what a "tight" trail is, what a "hilly" trail is, etc. So just because 5 other people tagged a trail as "tight" and "hilly", that doesn't guarantee that you will agree with their assessment. There's also the issue with the trail changing with time and weather that could cause older tags to become obsolete, but without any good way to "clean up" old irrelevant tags.
One feature I would like to eventually add, though, is the ability mark trails as personal favorites, and maybe also have a separate "wish list". I've already found myself browsing through the new trail guide, coming across a trail and thinking, "I'll have to remember to check this trail out sometime." Of course, I've already forgotten several of those trails. It would be nice if could just click an "add to wish list" button on a trail, and then later be able to somehow filter the trails to only show my "wish list" trails.
This info would most likely remain private to the user. I briefly considered that it might be good to show how many people have added each trail to their "favorites", but then I realized that it wouldn't really be an indication of how "good" a trail is, but more likely just a rough indication of how populated the area is around the trail.