Well thinking of the time these boards have been down I have wondered what the effects on a prime world might be if seperated from the planes and then suddenly connected by many portals to the planes.
Back on the Planes
For particularly religious-heavy prime worlds, I would imagine the religious situation would be similar to what occured on Krynn during the early Age of Mortals... when the various gods had been cut of from their worshipper bases.
Perhaps we would see some worlds foster more naturalist belief systems, those based around humanocentric ideaologies, or even types of inner spiritual beliefs to generate faith.
- Everyone is convinced the Apocalypse is here.
- The world suddenly becomes a battlefield for the Blood War, and the Apocalypse really does come.
- The mechanisms built deep within the world designed to act in tandem with other mechanisms on other worlds suddenly activate, and Balance is restored. Things that didn't use to make any sense suddenly make sense.
Perhaps the collapse of several of the prime world's religions and/or philosophies as well as a healthy load of culture shock to planar society.
Take the inhabitants faith in how the multiverse works and toss it into a blender.
If you wanted to take some inspiration from history, perhaps looking at the reactions of Native Americans to European explorers might prove to be a good source.