I might write one up for the smxi home page,
http://techpatterns.com/h2 (shortcut link)
That's a crude and somewhat outdated description, but it's not very readable because it's been expanded so often over time.
My current idea is to create a page that simply lists all the main sections with their functions, in a sort of hierarchical map.
What it does changes frequently, I add features, and now and then remove them, so the documentation has always been somewhat lacking and behind.
Basics:
system checks
kernel options
upgrade system
post upgrade options:
-package install
-package removal
-cleanup options
-misc tweaks (a variety of system tweaks)
-kernel option (same ones you see pre upgrade)
-virtual machine installer (starts the standalone module svmi)
-optional, if you start with -X scriptname#scripturl, will start any web based script you know about as an additional option in post upgrade options, for example: smxi -X extras#extras.webhop.net would add an option for the popular extras script, it would download it and start it when you selected that option.
and then the last step:
graphics install (interfaces with sgfxi, the graphics installer script, to tell user current available options for their video card type) sgfxi itself does the specific testing for card or kernel specific issues after it starts.
Most sections have subsections, so you can drill down, and back, into the options, using the navigation.
Obviously, the stuff most people will use most of the time runs either automatically or is at the top level of the navigation.