Back in 91 i was workin with a guy at panera with 4 sony xplod 15's in a huge azz box in his camaro, he had a sony 1000w going to each pair, each amp had it's own yellowtop. He really built the system right, except for his choice of sony equipment, which was probably only 1/2 his fault, and 1/2 the fault of the dude at best buy who sold him on it, it was a really nice install, and sounded pretty decent, sony being the only downfall.
So, if they're done right, they can sound ok, i'm sure if he had jl or something in the same install it would be 2x as loud, but if you don't know any better, you don't know any better.