Copyright and Fair Use

During our discussion on copyright and fair use in class today I started to think about when/how I might encounter difficulties using materials in my class. I realized that I have lived my entire life (almost) in the education world and almost everything I've done has fallen within the Educational Fair Use. In that sense, I've never really questioned what I've copied or how I've used it - I've always been a student and it always seemed OK. Was I right? In my almost 20 years as a student how many things have I copied or used that I probably shouldn't have? I'm certainly not regretful but it is something I thought about and probably will continue to think about as I prepare class materials and continue pulling things from the web...