My move into product marketing was an accident. (I mean, really, how many people plan to go into product marketing?) As a sales rep, I created my own sales tools, presentations, and demos for a product and shared them with my peers. Sales skyrocketed. I was asked to train the other salespeople in the company about my tools and techniques. Eventually, the VP of Marketing discovered what I was doing. He said, "Hey! You're doing the product manager's job. Why don't you become the product manager?"
Doesn't this happen in your organization, too? Sales reps are creating their own marketing materials because the marketing people haven't done them, or at least haven't created tools that the sales team finds valuable.
In manufacturing, there is a role known as the "Expeditor," who bypasses process to get an order out quickly to the customer. I find many product managers and product marketing managers are expeditors; they're constantly bypassing process to achieve a short-term goal. Salespeople tend to be this way, too. "Do whatever it takes to get the product to the client." But if every order must be expedited, the process is broken.
I find that good product marketing managers have a knack for finding patterns and addressing them with sales tools and customer-focused collateral. And great product marketing managers create a splash in the marketplace to let people know they've solved a pervasive market problem.