While the "railroad switch" idea has some potential, I think there's a problem that's already a bane to many players- you will end up hearing the same dialogue, over and over again, while you try to get to the small number of points that actually expand your options or move the plot. That there's a possibility you'll actually miss the chance to move the dialogue in the necessary direction just makes it that much more likely.
The thing is, though, that dialogue- especially expository dialogue- is frequently more about the needs of the designers than the needs or desires of the player. We need you to have this information to move the plot forward smoothly. Here it is. Not infrequently the player can't even move on, adventure-game style, until some subject lodged deep in the bowels of the flow-chart has been broached. Characters we ought to be involved with become, as Yahtzee said, "information vending machines"- ones we're as likely to be irritated with for standing arbitrarily in the way of our progress as we are to find endearing because we mistakenly picked the sub-branch where they tell us about their puppy.
It might actually be preferable to let the player get in over their heads and then have the NPCs offer to get them caught up; if nothing else, it would cut off that old contrivance "as you know, [so why am I telling you.]" Let the players stumble on without knowing the importance of Applied Phlebotinum to powering the Windsnurks of Cygnus-3, or understanding that the ambassador's robes clearly indicate his rank within his caste. If the characters were offering to help prevent us from making further mistakes rather than standing between us and forward motion, we might be more likely to enjoy their company.
