I never owned one.
But since I live in NYC, I see them all the time as its the Livery Cab/Limo sedan capital of the world.
I've seen some Town Cars/Crown Vics going strong @ 400+k miles in cheap livery service places.
They were like smoke screens/oil burners but ran well enough.
I've seen a couple torn apart at a mechanics shop i go to, and the main problems with them seem to be either:
A)Leaky/cracked intake manifolds.
B)Beat up chassis/busted rear air bags(due to NYC roads)
c)Failing COP's. Usually due to leaky intake manifolds.
Other than that, they are very good cars! And they can be pretty mean looking if you make them look like an CV LX Sport/Marauder.