I gather that UIQ is a front end for the Symbian OS.
Therefore can we install any piece of plain vanilla Symbian software that takes our fancy? I've only tried installing one Symbian app so far and that didn't work.
Installing Plain Vanilla Symbian Applications
No you can only install UIQ 3 compatiable software.
UIQ is the software / UI layer (middleware). Symbian is the underlying OS, but since programs use the UI ther specific to the platform (S60, UIQ etc.)