One of the difficulties for me, when it comes to making use of pre-prepared supplements or modules generated by other designers, is the lack of personal containment within the material. I always find that, with my own adventures or settings, lovingly designed (in fact, usually agonized over) from the ground up, learning the material in preparation for play is a non-issue: having generated the scenario internally, all of the pertinent details spring readily to mind at the table. This factor is, as far as I can tell, the MAJOR advantage of personal design as opposed to the use of pre-prepared supplements. DMing is just a much more natural process that way.
More and more lately, I find it essential to absorb as though by osmosis the work of others if I wish to use such work in a game. It isn't necessarily an issue of alteration of the details of the adventure, such as NPC/ monster stats or number appearing, or treasure or whatever. That process can work fine too. If I basically admire the supplement as is, however, and feel no need to alter it as such, a more arbitrary process of 'personalisation' works just as well. The idea is to, by some means, insert the delineated parameters of the scenario into the subconscious mind. As much of a time-wasting process as it might seem to some, rewriting passages or stats, or redrawing maps by hand, involves a higher degree of absorption than does simple reading or perusal- more particularly if the work is done with great care, with something approaching the loving attention devoted to ones own work.
So part of the process of prepping to run Joe's big dungeon has involved such efforts. These efforts, might, I add, have practical purposes of their own. For instance, as much as I love the wonderful dungeon maps that came with Castle of the Mad Archmage, I found that for my purposes both the quartered section level maps and the big poster maps were impractical for my game table- I want everything in my big folder, and all A4, with the maps removable and mountable on a screen. Using Inkscape, I opened the original maps, and by means of a process (I think it was edge detect- invert- moonarize- desaturate), I came up with an image which, if printed A4 at high quality, provided a detailed small version of the big poster maps. Then, by inking the walls, doors, numbers etc, a more pleasing and readily legible map becomes available:
Another example is Joe's redone City of Greyhawk map. I too have the boxed set for the city, but I definately agree that the version Joe offers, as being based upon E.G.G's Greyhawk, is indispensible for an awesome ongoing campaign based in the Free City. Now, Joe has a lovely colour version available, but, not wanting to fork out the cash for ink, and wanting my immersion-method to be engaged anyway, I'm hand-colouring/detailing the black and white map: