Are Project Managers Marooned on an Island?

Projects often pull people from different departments together to work on a project. While that is what the project requires to be successful, what does that mean for the people pulled from the different departments? Is the project of primary importance to them or is what's happening in their department of primary importance?

Business in Silos
When the modern corporation was formed, different departments were organized around specific functions. Accounting, Marketing, Sales, Finance, Operations and even IT all had separate requirements, required different skills and had different, recognizable paths for promotion. These departments offered structure, communications channels and common ground which was the basis for understanding.

Project management for larger projects, doesn't fit in any of those silos [Editor: we prefer the word department, thank you.] For a large project, people are drawn from across the organization, often temporarily, to work on that one project. Where is the common ground or structure?

Is PM unique?
PM often is unique, especially in organizations that are not focused around doing projects. Not only must the team get from NY to LA, but often times they have to invent the car, build the roads and put in the gas stations.

Not only does the team have to get from NY to LA, they have to go through the four stages of team development (Forming – Storming – Norming – Performing), usually very quickly.

What happens after the project?
All of this is very interesting, the question of whether project managers are on an island, but for someone with promotion aspirations, what is the next step after being a PM?

What have you seen?