My initial motivation for building the site was because when I was preparing for the Physics GRE there was such a void of information out there about the subject. Also, strange as it may seem, some of my most enjoyable moments in studying physics were when preparing for the Physics GRE. I learned an incredible amount of physics during my preparation efforts and it was a great experience filling in many of the voids in my understanding of the fundamental of physics and tying so many concepts together. Preparing for the exam was a great learning moment for me and if there were more resources readily available to me then I think I would have even learned more. I guess I see this site as a way that I can capitalize on this teachable moment called the Physics GRE because the grad schools make is such that students are extremely motivated to learn the material on the exam and I want to help how I can to make resources available to help students learn more effectively and efficiently and also to help students get into graduate school where they can learn even more physics.
Anyway, enough with the altruistic mumbo jumbo. I do make a token amount of money running the site in the order of a couple of dollars a day through getting a small percentage of every sale of items people buy when they visit amazon.com through the links I provide. However, the money I get does not even come close to justifying the time I spent creating this site but the funds can and do help me to justify spending more time developing the site into an even better resource. I get no money from having my Imaginary_Friend but he did help me to start the conversation in the forums out and helped to encourage others to post their thoughts which serves as a chain reaction to bring more people into a site which can translate to more visitors and hence more book sales. I am trying to find additional ways to generate revenue to this site but it is not really greed based but rather because I want to be able to justify spending more time developing this site into an even better resource for students.