It really started to come together for me when I used my own data too. The data in AW and Contoso is a little too perfect. That data is great for getting used SSAS but that is about it.
I also found that it helps to have a typical business question in mind when designing your cube. You want it flexible enough that you can answer the typical business questions plus some value added points (This way you can justify the need for the cube). If you try to pull in your entire universe of data and then filter it down, you will end up creating a huge mess. A lot of BI projects fail because the tool doesn't answer the important questions. it sounds like you already have an idea of what you want your cube to do though. +
It was definitely a priority to use my own data, for two main reasons:
1) I wanted one of the benefits of the development of the prototype to be some actual exploration of the data, not just by me, but by the executives and business analysts here, because I knew it would really engage their appetite for pursuing BI beyond the prototype. I also knew this would help with the justification for the conference expenses (registration, travel, lodging).
2) I knew that if I used my data, I'd be able to confirm that the results that the cube was producing were accurate.
"Nothing like sleeping in your own bed", as they say.