For the following, I assume: a non-small monitor (19" or more), use of a convenient mouse.
Desktop icons are dead. Why hide the important stuff behind all the windows?
For efficiency, every regularily used application has a fixed position that is accessible with a single click. (E.g. a window corner, or an icon in the dock.) Optional keyboard shortcuts are beneficial.
Layering windows does not hurt. Expose and similar features allow to get an overview, but (2) ensures we never need to dig for deeper windows.
Windows rarely get resized or moved once they have found their own position and size. Applications need to save their size and position.
Manual, effortless window managment is superior to automatic, but wrong arrangements.
It follows from (2), (3), (4), (5) that tiling has no real benefit.
There should be no distinction between starting an application and switching to it.
It should be possible to group windows into task-related, possibly overlapping positions. I may have a “web development” set that contains my editor and my browser. I may have a “typesetting” set that contains my editor and a PDF viewer. I want to cycle between applications in the current set easily.
Multiple sets should be combinable. I may want to typeset something while having my music player open. My window arrangement ensures I see enough of the music player without disturbing my writing. I want to toggle visibility of my instant messenger, nevermind what I do.
When switching between multiple sets is easy enough, the need for “multiple desktops” vanishes.
It should be possible to hack dwm (and maybe a bit dzen) into something like this. This is probably how dwm is meant to be used.
NP: LCD Soundsystem—Get Innocuous