In my experience the Product Owner is the most underestimated rol in Scrum. I think it's also the root cause of many problematic Scrum implementations.
Every Scrum implementation should start with the Product Owner. You should be very clear about the responsibility of the Product Owner:
- The product owner is responsible for the success of the product.
- The product owner is responsible for the long term vision of a product.
- The product owner is responsible for the release planning.
- The product owner is responsible for enabling a scrum team to implement the product.
This means that a product owner is much more than a user story writer. Most Product Owners i've met so far are requirements analysts with a new title. They are not empowered to sort the backlog, they are not empowered to learn from feedback and improve user stories.
If you are about to start with Scrum, start with the product owner. This will be hard enough, as many companies do not have a rol or person responsible for the succes of their products.