Once you've tried it you realize (as Jerry mentioned) 9/10 jobs (when playing AD&D) are much more easily done with pencil/paper and refr. the books; plus when using a computer you don't have those lovely records of what you've done scratches on paper etc., laptops are impersonal and bland. They are also solitary things, dragging the user away from the social matrix so key to the AD&D experiance (some say the point of the game) when used (even if your not drifting out of the group, your players figure you are..."are we so freakin boring you have to disappear behind that f...cking thing to get your fix", we've all been there).
Another big reason to keep Laptops away from your table is that they are strong icons of technology and thus pull your imagination out of the sword and sorcery setting into a more modern one (even subconsciously). Laptops at the table are just one more thing to kill immersion (even just sitting out).
But perhaps the most important reason of all (to outlaw laptops), is that a big part of the AD&D experiance is tactile and creative. Seemingly uniportant scribbles, sketches and writings by your hand (your character sheet, the group map, etc.) act as keys or portals to your imagination, visual cues, helping you enter and stay in a state of immersion (your personal imaginary setting), and to remain focused (as distractions constantly pull you out of your imagination into the real world). The core books also tie you to the game and your imagination (when I see the DM holding the DMG the cover reminds me of the setting, where I'm supposed to be). Paper and rule book reinforce your focus and your imagination....they hold the spirit of the game (the only visual proof of whats going on in your head); the act of thinking it, the impulse running down your arm to your hand and drawing it with marks is magical. If you really had a detect magic spell and you cast it upon a table of players, the rule books, maps, PC sheets, would all glow....for they all hold the spirit and "magic" of the game.
Next time you play with a laptop at the table, pay close attention and see it for yourself.
As for writing modules, drawing dungeons, I see no problem (but thats done away from the group). But at the gaming table, paper book and pen are like a fine artists paint, pallete and canvas. Sure, you can create computer art, it can look slick and clean, but its not the same experiance during the creation process....not by a long shot.
