Even at your dream job, you should be developing skills. It's funny, but we often stay in a job because of what we think we should be getting out of it, as opposed to what we are actually doing. There are some environments where being a personal assistant or working in the mail room will give you access to the power brokers who might get you a job someday. There are other situations where the only thing that working in the mail room is going to get you is a job as mail room manager. Take stock of what you are getting out of your job every few months and make sure that you are getting what you thought you signed up for. If you aren't doing exactly what you want to be doing, you should at least be able to point to some skills you are developing that are getting you where you want to be. If you are physically near what you want to be doing, but the opportunities for development aren't there, it might be time to look for greener pastures.