If I ever get around to building my 2nd sub to match my SVS PCi 20-39, then I will have something to really shake about.
The room will respond better with the 2nd sub, plus the acoustical panels will help overall, and the bass shakers are just fun. For those that haven't read my wordy build thread, I don't like to crank the shakers up too much, but boy do they help with things like a racecar's engine rumble, or a rocket/spaceship. You get the feeling of sub-audible LFE like nothing else, even when set pretty low.
M60s, VP180, VP150, QS8s, SVS 20-39PCi, HTPC, JVC RS45, Onkyo TX-NR709, Shakers