I have learned so much. Something that stands out to me though, is the sheer knowledge base.
I have learned that if I have a question about anything in the medical-school realm, chances are that it has already been answered on SDN. On the off chance that it hasn't, simply asking will often get you an answer, but beware, do your research first! Because if you don't, and your answer can easily be found using the search function, or worse yet if its sitting on the second page, you will be flamed to the ends of the earth!