I have a 10" in a '02 camaro (in the side part of the back well) and when I turn the bass up and put in my subwoofer mix mp3 disc it shakes pretty good.
I've suprised a lot of people when I tell them it's only 1 10", although part of it is because it's a small car and there isn't a barrier between the front and the back (ie: trunk or rear seats).
Anyway, the one sub shakes pretty good on its own. Enough to relax me when coming home from work
Someday I plan to replace it with 2 10" soloberics.