So the fluff is as follows: most planes are infinite, but the setting seems not to be affected by the infinity; the way between two places (say, gate-towns) seems to change and, at least in the Outlands, geography doesn’t follow the laws of geometry; travel times further change depending on circumstances: doing Evil in Elysium means you’ll never get anywhere, for the good guys everything is just around the corner.
Explanation: every infinite plane is actually a Schrödinger planar pathway that doesn’t actually exist physically until observed, at which point it assumes a form based on who the traveler himself is, where he is heading and the context of currently existing nearby terrain. Any actual place – town, divine realm – is a demiplane connected to the pathway, with the exeption that it counts as part of the larger plane for purposes of effects like Planeshift.
What do you think about this interpretation?
I've always thought of the "bounded infinity" of the planes as something akin to digits on a number line. Counting from 1 to 2 spans an infinite number of fractions, but those fractions have an easily defined boundary. They cannot be larger than 2 or smaller than 1. Infinity limited by paramters, but infinity nonetheless. While many planes don't have such clear-cut boundaries, I have always found the concept quite apt for explaining the idea of planar infinity. It's a rather Guvner approach, but sometimes that approach does make sense.
I don't know if I agree with the hypothesis for planar travel. It certainly applies to some planes more than others. A powerfully morphic plane like Elysium, perhaps. However, many other planes can have travel much like a Prime. By following certain rules and existing paths, you can reach Olympus or Thoth's Library or any number of locales. Part of it, too, may simply be the perception a plane places on those traveling it. In the case of Elysium, an evil creature might have a hard time not because the path warps, but because the plane disorients him and makes him get lost even though he thinks he's traveling in a straight line. A good creature, on the other hand, is whisked directly to his destination because the plane allows him to intuitively follow the most direct route.
http://kaitou-kage.deviantart.com/ -- My deviantART gallery
http://www.planescapemetamorphosis.com/ -- Planescape: Metamorphosis, a Planescape webcomic in the works