I've used Xmonad for a few weeks now and it is simply great: "screen real estate" is never wasted, you get free brain cycles by never doing the nitty-gritty details of window arrangement manually again - you switch high level "layout algorithms" instead that arrange your windows differently.

Are you (like me) an Emacs user? You want to remap the Xmonad modifier-key (default is on left Alt a.k.a. Meta). Here is my solution:

    xmodmap -e "clear Mod3"
    xmodmap -e "clear Lock"
    xmodmap -e "add Mod3 = Caps_Lock"
    xmonad

taken from my ~/.xsession file - this remaps the "Caps Lock" key as a "Mod3 key".

My ~/.xmonad/xmonad.hs looks like this:

    import XMonad

    main = xmonad defaultConfig {
             modMask = mod3Mask
           , terminal = "xterm"
    }

Now I can use Caps Lock as Xmonad modifier key and Ctrl/Meta as I'm used to for Emacs (note that I have a PC 102 keyboard - if you have a keyboard with "Windows"-key you might use this key as modifier key instead and perhaps remap Caps Lock as your Control key...).