Hmm... Something like missile launchers, maybe.
Wait, you can't add force in lua, can you? Damn, that'd be fun...
Can you change the strength/movement speed of joints? If so, a Temporary Superstrength script would be cool.... press Q or another key, and you become stronger/faster for the next... 20 frames, or so? Would be nice, and could lead to some very interesting grab situations.