Having read this whole giant thread, I agree wholeheartedly (I think) with RC, Hussar, and Quas. Now let me go ahead and shoot my mouth off
The primary goal here, I think, was: What is railroading and how does it relate to d&d as a storytelling medium? So, in an attempted answer:
1) Railroading is (as others have stated) the DM usurping player control of their characters' fates in unprecedented and arbitrary ways for the purpose of furthering his private goals. Railroading is
always a
bad thing(tm). Railroading is
sometimes an
acceptable thing. To make analogies: murder is always bad, but sometimes is acceptable; lying is always bad, but is sometimes not only accepted but expected. In all such cases, the bad behaviour becomes acceptable when it serves a greater good.
Railroading is a purely local phenomenon, IMO. The sort of macro-railroading that Rounser and others have a problem with I have difficulty even comprehending as railroading. I've only played in two campaigns where the entirety was mapped out adventure-for-adventure beforehand and, in both cases, that was
why I played. They were A Night Below and The Rod of Seven Parts, specifically. In no other campaign I've taken part in or heard about has the DM had a series of adventures laid out end to end without said adventures being, in truth, all part of one large adventure which the players agreed to take part in at the outset. Perhaps the players decide they no longer enjoy the adventure partway through, as was the case when we played A Night Below. After several months of adventuring we were no longer having fun with the campaign and the DM no longer had fun running it. We aborted it and took up a new one. I can't imagine a case where a group decides they don't like a campaign and the DM forces them to go along with adventure after adventure.
Railroading, in my definition, occurs when PCs wish to take a course of action which, for one reason or another, would throw a monkey wrench in the DM's plans. Easily circumventing a trap that was meant to diminish their resources before an encounter, killing the BBEG with a lucky shot during a non-final encounter, exploring an area that the DM has absolutely nothing prepared for. DM fiating the situation back into control is always bad because a good DM should be capable of rolling with the punch. Sometimes it's acceptable because
not fudging it has potential to ruin an entire campaign. Sometimes the PCs
have to step through that magic portal or listen to that crusty old-timer in the bar.
Other issues, like pet NPCs who trounce the PCs for no apparent reason or baddies who always know precisely how best to take advantage of the party's weaknesses and instantly adjust to the PCs' changes in tactics are not, by my definition, railroading. They're bad, certainly, but they're totally different issues.
HappyElf keeps bringing up "power issues" when trying to define railroading which, I think, is telling of the disconnection between HappyElf and the rest of the posters on the thread. He/she has problems with a lot of specific things that (presumably) DMs have done to him/her in the past (charm/domination for exorbinant periods, continual party capture scenarios, etc) which all certainly reek of a DM with dominance issues. They will surely cause a group to break up but they aren't inherently railroading. Domination, kidnapping, imprisonment, and the like certainly can be used to railroad, but they're a method not the problem. Yes, it's a matter of semantics but that's the point. Terms get thrown around a lot here by people seeking advice. "Am I a railroading DM?" "Are my players munchkins?" It's important to know what these terms mean in order to offer constructive advice. Maybe the DM in question
doesn't railroad but is still guilty of using over-powered NPCs and DMPCs. That's a whole other issue and should be dealt with a whole different way.
And specifically to HappyElf: we're not discussing the issue in order to let bad DMs off the hook. A DM who keeps a PC charmed for a full session, much less several sessions, without the player's consent is a Bad DM. He may also be a railroading DM, not necissarily, but he's most certainly bad.
2) How does railroading relate to storytelling in d&d?
The same way that railroading relates to everything in d&d. It can be used to reach a goal, but it is rarely necessary. The bit at the beginning of the WLD is necessary, acceptable railroading but it's barely part of the story. It could be the first sentence of a multi-tome epic fantasy series: "The heroes stepped into the dimness of the cavern and the enterance sealed itself silently behind them."
I can see where someone could feel that railroading is necessary for storytelling. If you have a plot laid out before-hand with certain points which must be hit along the way, then yes you'll likely have to railroad on occasion as it's doubtful a group of 4+ humans will accidentally drive themselves into your waypoints.
However, it's a perfectly viable proposition to state that a story can develop purely through player reactions to spontaneous (or at least semi-spontaneous) DM challenges. A party enters an old tomb and, finding themselves terrified by the prospect of dread ghouls and life-devouring ghasts, turns and flees. That's a story right there. It's kind of a lame story, but it's still a story. You could say that in order to tell the story of heroic warriors striding boldly into the dark and slaying the Lich King the door had to magically vanish and all potential means of egress become null and void. Maybe it's like the WLD and you're right, or maybe you could just toss in a local bravo at the tavern boasting of the easy pickings in the Lich King's tomb and the pushover undead to be found there. The party won't realize until they're surrounded by wights that the trinkets the bravo flashed were cheap fakes to bolster his reputation (unless they've got a good Sense Motive) but by then it's too late.