I came across a few videos of Portal 2 co-op over the weekend. Here’s the first one of the set of four:
The videos confirm that in co-op there can be 4 portals (2 per person) active at the same time. Also shown is a bridge that extends from some point that goes through portals, so you can have a platform sticking out perpendicular to any surface you can put a portal on when you can portal from the target of the bridge generator.