Nearly every volunteer experience I've had has been good. I've worked with animals, in libraries, and reading for the blind, and the positive feedling of doing something worthwhile makes all of those daily moments of frustration or bordeom in life much easier to accept. Having said that, my biggest piece of advice is to investigate the place where you're considering volunteering as much as possible. The most important factor is whether you have good fit. If the organization doesn't have something that you really want to do, you're going to resent the time commitment. Fortunately, there are so many volunteer opportunities out there that you should be able to find something that fits well.