I found that to get micign's stuff working in my Ubuntu box, I needed to change this line:
CXX_MODULES += $(shell find $(ARDUINO_LIB) -maxdepth 2 -mindepth 2 -type f -name *.cpp -exec /bin/echo -n " {}" \;)
to this:
CXX_MODULES += $(shell find $(ARDUINO_LIB) -maxdepth 2 -mindepth 2 -type f -name '*.cpp' -exec /bin/echo -n " {}" \;)
putting *.cpp in quotes, otherwise find wouldn't pick up any of the files
EDIT:
The original build error I was receiving was something like:
blah/applet/main.cpp:xx: undefined reference to 'SomeCustomLibrary'