Fang asks, What Makes the Perfect Gamemaster? .
It is having fascinating world, scenarios and characters? Being able improvise, but not railroad? Perhaps if one lets players act whenever / however they like? I’m a big proponent for keeps things moving; is that it? Maybe a perfect gamemaster can handle a split party with perfectly equal spotlight time? Memorizes all the rules? Is fair to the players but not the NPCs?
I like his required skill set, though they’re as impossible to reach as perfection implies. The linked post has some great advice for answering the first question: for creating and sharing a fascinating world, characters, and scenarios. Read his article  for a fascinating way to create and share and exciting setting, while I hunt down some leads on the other questions.
Being able improvise, but not railroad? If you’re looking to react to the character’s plans, you need several things. One important, but often overlooked, required element are proactive characters. If the PCs don’t do anything, there’s no spark for improvisation. If your characters are poking and prodding at the scene (here’s a great article from Heather Grove  about encouraging this), then it’s time to improvise. Take a look at Patrick’s advice on the subject . (Or commenter BryanB .)
Perhaps if one lets players act whenever / however they like? This may tie into questions about characters do you allow evil characters? , or being jerks (argument #3 from this post ), but let’s set those “bad apple” cases aside for a moment.
Letting players act whenever and however they like is normally associated with sandbox play . The plot, if any, is in the background and the spotlight is on the characters and their actions. The world responds organically to their actions– NPCs react to the PC actions, rather than having a quest to carry out. The characters get into whatever interests them (or their players), when they get around to it.
I’m a big proponent for keeps things moving; is that it? If you’re looking to keep things moving, keep an eye on Walt’s suggestions for Short Sessions . Take his advice and you’ll dramatically streamline your sessions. Even Dr. Horrible  can teach you about pacing. But if you want great advice for pacing, let Fang walk you through The Most Important Gamemastering Tool .
Maybe a perfect gamemaster can handle a split party with perfectly equal spotlight time? Troy’s spotlight encounters  discussion is great for helping you figure out how to make individuals shine, split or together. Walt has great advice about managing subplots . Martin’s recent post about White Wolf Preludes, Round Robin Style  is a perfect example of spotlight management. It will serve you mid-game as well as it does kicking things off.
Memorizes all the rules? Knowing the rules makes a game go more smoothly– no argument here. Still, Sometimes to Run a Fun Game You Need to Ignore the Game . Besides, there are other rules that aren’t in your book that may be just as important to your game. Like the Rule of Fun  and the Rule of Cool .
Is fair to the players but not the NPCs? This too is important. Who wants to show up to a game where the GM plays Calvinball, changing the rules at a whim to mangle the PCs? Of course, “fair” is subject to a lot of debate– fudging die rolls, inter-player balance , and even which scenes must be played out .
So that’s the crash course to make you the perfect GM. Let us know if it works!