What does a product manager do?

I was hanging out at New York Night Owls a couple of weeks ago and started talking to Campbell McKellar about Loosecubes. She has an awesome product that just launched, and I think a generalist product manager will help her scale. At the time, I described in words something similar to the following divisions of labor and how launching a site affects those.

Pre-Launch, the founder has tons of time to worry about the product. Even if they are not experienced in product development, they have time to communicate needs and scheduling deliverables with the design and development team. After launch, say goodbye to all of that time spent making thoughtful decisions!

Your design and development time is your most expensive and precious resource. You're wasting it, but it's not your fault. Building a good product is hard, requires a ton of focus and mental energy. All of your time is being sucked away to answer questions from VCs and develop the relationships with customers that you'll need to succeed. But be careful. As you go further down the chain towards development, the more expensive mistakes are to fix. You'll never get things right the first time, but I effective decisions are rarely made in haste.

So, what's the solution?

A product manager enables the team to execute the company vision.

The founder communicates the vision to the product manager, and they work together on strategy. Implementation of the strategy is left largely up to the product manager. Where the founders responsibilities end may vary depending on experience of the Product Manager, but the ideal situation is that the PM is an extension of the Founder, and is better able to communicate to the design and development team "what should be built next".

This hypothetical I describe above is the way things work at ChallengePost. Brandon is a non-technical founder who is inspiring to listen to during pitches to customers (insert sell ice to eskimos reference), but there's no way he has the time between phone calls and business trips to direct the product. So when I joined, Brandon was able to shift his focus gradually away from the product so that our discussions are primarily about strategy; should we do this or that, rather than execution; how we do this or that.

I'd love to hear about similar situations. What has worked for you?