You know, Best Red does make a good point about the distinction between a warning log. "Watch out, there is a fair amount of broken glass in the area. I think this location is sometimes a bit of a party place" versus a critical log "What sort of a moron hides a cache in a place known as a local party spot?"
Obviously my two examples are extreme to point out this difference. However I go back to my original point that different people have different standards of polite. (Heck, I'm Australian. We use the "toilet". I learned very quickly in Canada it is not polite to say that, instead we use the euphemism "washroom" here.) What I may think is ok, someone else may perceive as rude. Some people will take any comments as a criticism of their cache. And heck, sometimes they should pay attention to that.
Getting personal, as Best Red points out, to me is the line in the sand. "Finding this cache may not be safe after 6pm" is ok but "The cache owner may want to rethink having a cache here" is a more personal comment. It is possible to rephrase any criticism in a non personal way and still get their point across.
Go on try it. As a school teacher, I find I have to rephrase a lot of the time. For example, I use "the course material is presenting some challenges to your son at the moment." Guess what I could have said instead.