I would like to see any mouse button as modifier. I would like to replicate mouse gestures with this, such as hold right mouse, click left: send cmd-left (back) or hold right mouse, scroll wheel: send cmd-(shift)-tab.
I've only a few days left in my trial. This is the main feature I use BetterTouchTool for (currently dealing with a slightly annoying Windows Key+Left/Right click to change desktop on Mac) so it will probably decide whether I purchase or uninstall.