I spoke to an organisation recently that was having trouble with a lack of clarity on backlog items. When I asked how their Product Owner (PO) dealt with that, I was told that he was only allowed to make decisions on two out of five modules of the system. The remaining modules were the responsibility of two other department heads. This was creating an inertia with some features that could not be developed because decisions were late in coming or in many cases had not been made at all.
It is easy to criticise the PO, but he had not been formally trained as a PO and he was not being supported in the best way by his managers. They could have cut through the internal politics and supported him better by empowering him to make all decisions.
I am a big fan of Roman Pichler's book "Agile Product Management with Scrum", and if this PO in question had this book in his toolkit he would at least have known how to theoretically manage a lack of clarity in his backlog items and how to identify his major obstacles.
Needless to say, a POs role is multi-faceted and challenging and can change depending on the type of product, what stage the product is at in the developement lifecycle and of course he is highly dependent on the scrum team. Organisations are still quite new to the concept of a PO and often neglect to understand the true purpose of this role and instead delegate the responsibilities to that of a traditional Product Manager. It is part of my role to spread the message of the benefits of a well trained and empowered Product Owner and I look forward to the day when every organisation I speak to understands the true nature of this role.