In a nutshell, that is what a PM's job is all about. Taking responsibility for the product, its launch, its features, its ecosystem; making decisions. Making decisions is a large part of my day. Making decision with half information is almost all of it.
Someone asked me how does Google integrate its various functions like marketing, patenting, partnerships, legal, Ops etc so that they work for the product in synergy. The answer is: Through the PM.
The PM owns the product, all the functions work for the product. There is no direct reporting here, however there is one guy who is the common thread between all these functions and it is the PM. Invariably, there are decisions that need to be made at a macro level that define the work and strategy of these sub-divisions. Those decisions are the domain of the PM. Once the structure is set, then these divisions have a free reign to set their agenda. This is how Google manages a flat hierarchy yet ensures efficiency.
It makes one person's job incredibly tough. Mine. I spend all my day surrounded by folks who know more than me, but who look towards me for structure. So I have to learn how to think very fast, ask the right questions, and make quick decisions. Almost always the plan I put together needs significant tweaking. However, more often that not, a plan is better than none. Hence my value-add to the product.
A lot of people worry that the PM has all the responsibility without any authority. On the contrary, my experience has been that most people are so glad to have you on their side, providing structure to the chaotic product that they are trying to put together, that it has never been difficult to influence people to get stuff done.
The bottom line is - People do not like ambiguity. Anything (anyone) who helps decrease ambiguity is welcome and a strong asset. In Google, a PM provides direction, vision, and creates a framework on which multiple teams put together a product. It is the job of a CEO-in-training.
Its midnight, I am still working but I love every moment of what I am doing. Its been three months for me out here at Google, and thankfully, I can say now that regardless of whether this was a better decision than going to VC (that time will tell), it definitely was not a worse decision. I love my work, and that is more than what most can ask for.