Yes, I always used to say God came to earth and said, hammer 3.4 for half life, what's this now? And then he sat down and made Carbaseus before ascending back to heaven.
Cstriker I can tell you what i've learned so far. Good mappers seem to map with a crazy obsession in detail, geometry, texturing, layout and everything. Some like Kasperg and even Hondo just practically go crazy with random geometry. Things that should be symmetrical are, but not completely. Where one door exists, two exist above it. Geometry bevels out "when it feels like it". And lights go, "wherever the hell they want". Or where they will get a good light flush into the space. Sometimes things line up as expected, but in EndlRainSH certain textures don't which leave you never remembering the detail aspects giving the map a new feel everytime you play it. Unless you look as closely as I am.
People who are random in their mapping map with freedom, mapping fast.
I picked up a Dr.Seuss book last night "oh the thinks you can think", and read it. "just for memory sake". The last page said "Think left and think right and think low and think high. Oh the thinks you can think up if only you try" Well I can't deny that this quote does apply!
Thinking about your map as a layout or in plan "above view" is only one perspective. It shows horizontal relationships. But in the 3d world of hammer you must consider your map in all three dimensions. Oh, and do so with a crazy obsession! Frank Lloyd Wright himself said that it is extremely important to draw architecture in 3d. It makes sense to plan maps in plan, elevation, 3d, and even in idea which you can simply write. It is how I designed my dream mod "wrote out a story". Any means of design you can possibly apply, you should.
I'm pretty sure some mappers sort of lay out a plan and sort of consider vertical elements and then begin mapping away designing the geometry as they go, maybe having done some sketches before hand or along the way. In this case I believe Kasperg uses this method like in floatingline. Other mappers who aren't doing it as an exercise and want to put out for example one super fantastic map like K7's Carbaseus or Hondo's EndlsRainSH use the more obsessive method paying every attention to the layout along with detail, geometry and so on.