I am having similar problems. I bought a shuttle last night, installed the plugin but it doesn't work and there is no way to tell if Mach is actually seeing it or not. I updated to the latest Mach lockdown and used the current plugin...
I initially tried it without installing the shuttle driver, then installed the driver, then later uninstalled it. I only configured a few buttons (set x,y,z,a, ++ ---) but I couldn't find anything that gives an example setup so I can't be sure that I have configured it properly.
I searched the Yahoo group, cnc zone and here to no avail. I imagine I will figure out what is wrong eventually...