Scotty, calm down.
Scotty is right in most of his points. It's just not a good idea to have parts of your OS on removable media, independent of the OS. Be it /usr/local, or c:\program files, or whatever, sooner or later you run into big trouble when you put it on removable media.
The idea I proposed somewhere in this thread (with the zip, er_registry fragments and boot scripts) specifically is that way for such reasons. It doesn't address the unmounting problem tho.
Alas, there is a need for quick&dirty apps, in the sense of "download; tar -x; configure; make; make install" without touching the app's sources. This is not too useful and will not produce "real" Iliad apps (different UI logic, clumsy xlib hack instead of real updates, etc), but works. As long as everybody knows this is a dirty hack and begging for trouble, i.e., makes a location-independent installation package once the app becomes "stable", the /usr/local hack should be okay.
And Adams proposal was much, much, much better than those that just wanted to make random directories without any sense for Unix/Linux fs logic, e.g., "_libs" and "_sharedlibs" (*shudder*).