There are so many factors to take into account when answering this question. First of all, it depends on the potential reaction of parents in the area. If you live in a more reserved area, they might have a harder time with the adult themes that are presented in the novel. Also, another factor is what grade it is being taught to--it is much more appropriate for seniors than for freshman, for example. One last factor is one that brings the teacher into it--how will they teach the novel? How will they handle the more disturbing elements contained within it? How will they approach the very intense moral elements?
Other things to think about are whether or not you feel that teenagers can handle some of the issues presented--the sexuality that is present in the novel (especially seen through Curley's wife), the killing of Lennie (which is very upsetting), the constant vying for position between the farm hands--these things can be disturbing, difficult to comprehend, and potentially distracting for kids that are at a younger age.
All of that being said, there are some really worthwhile themes, issues and areas of discussion presented: friendship, loyalty, our stereotypes of mentally handicapped people, depression, loneliness, abuse, hard work, the concept of mercy, and what truly makes a life worth living. All of these issues are presented in that story in such a way to facilitate very in-depth discussions about some important issues.
One should take all of those issues into account when deciding whether to teach it or not. I hope that helps; good luck!