I have 3 different kinds. My oldest (DFPs) were made in '88, and are 2 different consistancies of foam. Both fairly soft. They are only partially posted, but only with the same foam. While thay are comfortable, and I have strait knee and ankle joints (no rolling or pronation/supination), they made the ski boots react more slowly to fine input. However, they work just fine in my roller blades and soft snowboard boots.
Then I decided to go rigid. Basically, they are hard plastic, covered with a layer of neoprene, done by an orthopedic. They aren't posted, but don't need to be, because the plastic is so damn stiff. They also only go forward to the front of the arch, then the neoprene continues with a piece of foam under it. I don't like these, because they are too stiff (hard), and are not full length. I can feel the front end of the plastic, and it bugs me. Also, they don't have the toe impressions, which I like, because I feel like I can "grab" with my toes if I need to, and get a bit of control from that.
It didn't take me long to decide I didn't like those, so, only a year later, I got a pair of top-end cork Superfeet. I love them. They are warm, comfortable, firm enough that input from the feet is immediately transferred to the boot, and yet soft enough that they don't hurt. Cork is good stuff.
I originally tried to get a set of Peterson cork beds when I got my first footbeds (the DFPs), when I was living in Summit County. But the bootfitter sucked, screwed them up twice, so I got my money back and bailed on him. At the time, the DFPs were probably better for me than cork anyway, because I wasn't advanced enough to really want every little bit of input going to the boots. But who knows, maybe they slowed my progress?