Most windows managers out there are windows oriented, so that you have single desktop and many overlapping windows. This is true for MS Windows, Mac OS, Gnome and KDE. There are ways to set up several more workspaces, but most people would continue to use in windows-oriented style as all running applications would still be represented in task bar.
If you think about it, the windows-oriented workflow has great overhead, in resizing windows, looking for application in the task bar or list of applications and managing misplaced overlapping windows. Working with more than certain number of applications becomes unfeasible, as the overhead of managing so many windows becomes unbearable. There are many band-aids to minimize number of open windows, in form of tabs (especially in firefox or konsole), lame attempts to integrate many application in the same window (as mozilla thunderbird does) or hiding the application and it's interface into tiny icon in the status bar.
Ideally, one needs not to think how to switch to the application he needs to access. It would be even more desirable for the application to launched automatically if it is not running already. The desktop should be organized so, that it would not matter whether you have couple of windows opened or many hundreds (provided you have enough resources).
After experimenting with many approaches, I would like to share with you one that works good enough for me.
The venerable fvwm2 window manager, albeit being very old, remains highly configurable one. The configuration uses text configuration files, that allow user to customize look and feel of the window manager up to the low-level details, such as autofocus of windows or executing a shell script on magic keypress. The features are pretty important for the workflow described.
Easiest, immediate, switching to application of interest is by using dedicated button. Actually there are many keyboards that have additional buttons, just for that purpose. The approach has several issues, such as limited amount of buttons, predetermined functionality (psychologically aggravated by inscribed picture on the button) and dependence on the keyboard in use.
Software buttons, albeit requiring a bit of learning, look much better in this regard. If you use a combination of CTRL, ALT, SHIFT, CTRL+SHIFT, ALT+SHIFT modifier buttons together with the numeric buttons on grey part of the keyboard, you can easily get 45 "hot-keys".
Once you get 45 "hot-keys", you can create 45 workspaces, arranged in blocks of 9. Module of fvwm2 "FvwmButtons" shows them nicely in a corner of the screen:
The bright rectangles are already open windows. You can drag them from one workspace to another using mouse.
Now, as we reached the goal of instant switch to any workspace, each workspace can be dedicated to hold window (in rare cases couple of windows) of an application. For example, you can assign workspace ALT+Grey7 to a internet browser, and workspace Alt+Grey1 to a mail client. After several uses you would learn the hot-keys by heart, like you remember your password (which you can always type but not always remember).
The above scenario assumes that you launch the application in the dedicated workspace manually. Flexibility of the fvwm2 window manager allows to make each switching keypress to run a shell script, that would check whether the workspace already runs the application it was dedicated for, and, if not - automatically launch it.
This is exactly what I did as you can see in the configuration files over here.
As a added bonus, my auto-execution script checks hostname of the computer I am working on, and takes it into account when populating the workspace. For example, one of my workspaces is automatic ssh to the firewall, which is only accessible from inside of the corporate network. On my home computer, switch to the workspace would not launch anything, as it would be pointless.