Do you read the whole module beforehand and only glance at the module during play when you need to?
Yes, I read it all. Sometimes multiple times (specially the larger ones, like RttToEE)
Do you study it so much that you remember everything?
I study it so much so as to have a "holistic" view of the module. To have a feel of how it works, or should work.[/b]
Do you skim over the module just to get an idea of what to expect and basically learn it as you are running it?
Never. I don't trust modules that much
Do you study the module first and just run what you remember and wing the rest?
Never. That's what I buy a module for.
Is it frowned upon for a DM to quickly review a portion DURING the game because he forgets the details?
As long as it isn't frequent, I wouldn't frown at that.
And what about running a huge module that's 150 pages or more? Do you study sections of it between each session or do you learn the whole module and then run it?
As mentioned above, I read it multiple times, but also prepare before the session.
Do you usually study several adventures at once so you can use multiple scenarios in the same game so players don't feel railroaded? For example; you study 3 different modules so if the players start to head in one direction that is part of adventure A, and then take a turn down Adventure B because you presented the opportunity, they can end up taking a turn down Adventure C and they won't feel railroaded.
I prepare one at a time.
But if I finish preparing a module, and my players haven't started it yet, I sometimes begin to prepare another thing, so they can choose.
So, basically, I prepare one module at a time.
Oh and my last question, do you take notes while studying a module, and if so, what kind of notes?
I should. But somehow, I remember most of the "notes" I make.
I usually fix things that don't make sense.
Give more depth to the plot, the NPC's and the surrounding terrain/towns/NPC's, things that aren't part of the module, but are near it or affect it.
Sometimes I rewrite descriptions to enhance certain aesthetic aspect or mood.
Yes, I read it all. Sometimes multiple times (specially the larger ones, like RttToEE)
Do you study it so much that you remember everything?
I study it so much so as to have a "holistic" view of the module. To have a feel of how it works, or should work.[/b]
Do you skim over the module just to get an idea of what to expect and basically learn it as you are running it?
Never. I don't trust modules that much

Do you study the module first and just run what you remember and wing the rest?
Never. That's what I buy a module for.
Is it frowned upon for a DM to quickly review a portion DURING the game because he forgets the details?
As long as it isn't frequent, I wouldn't frown at that.
And what about running a huge module that's 150 pages or more? Do you study sections of it between each session or do you learn the whole module and then run it?
As mentioned above, I read it multiple times, but also prepare before the session.
Do you usually study several adventures at once so you can use multiple scenarios in the same game so players don't feel railroaded? For example; you study 3 different modules so if the players start to head in one direction that is part of adventure A, and then take a turn down Adventure B because you presented the opportunity, they can end up taking a turn down Adventure C and they won't feel railroaded.
I prepare one at a time.
But if I finish preparing a module, and my players haven't started it yet, I sometimes begin to prepare another thing, so they can choose.
So, basically, I prepare one module at a time.
Oh and my last question, do you take notes while studying a module, and if so, what kind of notes?
I should. But somehow, I remember most of the "notes" I make.
I usually fix things that don't make sense.
Give more depth to the plot, the NPC's and the surrounding terrain/towns/NPC's, things that aren't part of the module, but are near it or affect it.
Sometimes I rewrite descriptions to enhance certain aesthetic aspect or mood.