To be honest, before the advent of the Planescape setting I never even considered actually using one of those outer planes in play. For me they were just part of the setting's background.
Part of the reason was the difficulty of traveling to those planes and an even bigger part was the difficulty of surviving there once you got there. Besides I always found it difficult to think of a reason why anyone would want to go there.
Now, in my current 3E campaign I've decided for the first time to actually play a couple of high level adventures out there.