For those that want to go the route of editing their XBMC keymap file this URL has 2 useful utilities for Windows users: http://xbmcmce.sourceforge.net/
There is a showkey.exe that will give you the exact line of text you need to add into your keymap.xml file and it works great as a key tester. It's better than opening a word processor since it gives you information on key modifiers ctrl and alt. There is also a program to actually help you create the keymap.xml file itself although I prefer to hand edit the file.
It goes without saying that with all the extra keys you can add lots of extras.
My example above added 4 options for power. Suspend puts the computer to sleep. Reboot will reboot the computer. Powerdown powers off the machine. Shutdown is slightly special. It automatically performs the action defined in the System -> Settings -> System -> Power Saving -> Shutdown Action. So this could sleep or power off the computer depending on what you configure.
I like having a key code to reload the keymap so when I edit the map I can test out the key immediately in XBMC without reloading XBMC. Also, if you have a typo you have a chance to fix it and reload again.
Here are a few other uses for the extra keys I've added to the global section:
<f1 mod="alt">ActivateWindow(Home)</f1>
<f2 mod="alt">ActivateWindow(videolibrary,movietitles,return)</f2>
<f3 mod="alt">ActivateWindow(videolibrary,tvshowtitles,return)</f3>
<f4 mod="alt">ActivateWindow(MyVideo,files,return)</f4>
<f5 mod="alt">ActivateWindow(MyPictures)</f5>
<f6 mod="alt">ActivateWindow(MusicLibrary)</f6>
<f7 mod="alt">ActivateWindow(Weather)</f7>
I assign these to the soft buttons on my Harmony. This allows me to jump to Home, Movies, TV Shows, Video Files, Pictures, Music and Weather in that order.
If you want to know exactly what keys do what in XBMC, this link shows the default keymap.xml file for XBMC: https://github.com/xbmc/xbmc/blob/master/system/keymaps/keyboard.xml#L39