Product Management is something that should be easy to understand. The highest level goals of product management should be easy to articulate.
1) build a valuable product
2) maintain the value of a product relative to its customer community
3) manage the investment in the product, to ensure the best possible return
I believe that these goals are universal to product management across all domains, and all situations. I don't know that I can add anything that is not a derivative of one of these goals. There are many product domains, and many situations. The domain that I am most familiar with is software, and even within that domain, there are many situations:
- commissioned custom built software
- shrink-wrap software
- vendor vertical market software
- vendor highly configurable software frameworks
- software as a service
- open source software
These situations are different primarily because of different relationships between the customer community and the product manager or the customer community and value. In all cases, the product manager needs to understand who the customer community is, and what is relationship with them is based on. He needs to develop deep relationships in that community so that he can understand and articulate what that community values and so that he can discern changes in what the community values over time. He also needs to understand the flow of investment ($$$) into the product, and how that relates (or does not) to the customer community.
The product manager must be an advocate for or champion of the product, helping the customer community understand how to get value out of the product. Sometimes this is education, sometimes it is marketing, sometimes it is solution consulting services.
The product manager needs to understand and direct the "delivery" organization by communicating the sequence and pace of value delivery. Explaining the value of each deliverable to the delivery team, expressing the customer's perspective.
The product manager also needs to understand the technical risk arising from the delivery process, and communicate that to the customer community, effectively managing their expectations of delivery.
Overall, the product manager is the interface between the customer community regardless of how that is organized and the delivery organization. The product manager must adapt to the organization of the customer community, and the management processes in use by the delivery organization. She does not have control over either one, and so to be successful, she must learn enough about the delivery process to be effective, and she must build relationships and trust within the customer community as well.

