I cannot fathom why one would need as many as 8 virtual desktops
I'd probably drive you crazy, then.
I run Enlightenment, with my pager set to 4x8 - four desktops wide by eight high - and the only reason I don't do 8x8 is because then the pager would be wider than gkrellm and steal more horizontal space on each desktop. At least two of my brothers are much the same way.
What do I do with all of them?
Partly I do what someone else mentioned, group related windows for the same task together.
Partly I have a few dozen maximized xterms on different desktops for convenience purposes. (Some of them are just there by habit by now, but I always have uses for them.)
Partly I like to be able to have multiple browser windows for different sets of tasks - particularly so that when one task requires opening an ungodly number of tabs, it doesn't shrink the tab width beyond usability or push the newest tabs off the right edge of the tab bar (requiring scrolling).
Partly I like to know that I can always jump to a new desktop, open a new xterm and have a clean (usually temporary) environment to work in, without colliding with any of the other things I have active.
I get by at work in Windows, but there I'm rarely doing more than three things at once, and most of them use the same programs. For the sorts of things I prefer to do on my own time, I'd chafe at as little as the four desktops which are the default for some LiveCDs I've tried.
You know you can close applications when you are not using them, right?
Of course, but when you're probably going to go back to them soon and it takes work to get back to the "ready to do the next thing" situation after opening the program, why would you want to?
On the original topic: I don't care about desktop environments. I turn off all the graphical frills of Enlightenment, set the desktop background to black and disable anything resembling a screensaver except for simple screen blanking. I certainly don't use a program-launcher menu, and I don't care what source a program comes from as long as it fits what I want.
I haven't changed window managers in at least ten years (unless moving from E16 to E17 counts), and I'm not likely to soon either; getting this one configured to suit me is enough of a hassle, I've got no real desire to try to do it with another one when I don't need to. I do want to experiment with other WMs, in case one would happen to fit my needs better, but not badly enough to shut everything down and restart X for the purpose - and I don't yet have a place to hook up a spare machine to test such things on.