Salomon 1080 foil has been wood core for the last couple years http://www.salomonfreeski.com/others/ski/skis/freeski/teneighty.html - maybe the last model was 06-07 with the white ski with party letters. Way back in the day, Salomon used the cap of the ski as the structure. The cap would also control the behaviour of the ski - stiff, soft, quick, kick. So the core was supposed to be only filler. Everybody was trying to build an inexpensive yet quality ski. I think that all manufacturers have pretty much since shifted back to the core being an integral part of the ski and have gone back to wood and maybe some space age stuff like carbon stringers...etc. Foam was good because it was consistent. Wood varied from tree to tree and often had a different flex. I think Volkl had their own forest. I heard some racer's father picked a tree from their farm for his son's skis.... Wood can rot when wet. Foam doesn't.
Foam core is good for light weight riders, riders with finese style, and juniors / kids and as a lot of people have already written it cannot take getting hammered or have kick like good wood cores. Foam is not for aggressive riders or heavy use.
Wood cores can also be crappy. They can be overly heavy and damp. So it ain't your wood but how u use it. A few companies were using plywood cores as an inexpensive way to produce a low cost ski. A lightweight strong wood core is expensive. Wood has so far been better to screw in and hold the bindings. Everything has it's place.