Thanks for your comment on my "Pedaling a Bulldozer - Fat Bike" blog. You mentioned see a person on a fat bike bouncing along. Bouncing on the big high-flotation tires can happen with a fat bike.
There is some skill required to ride smoothly on a fat bike. However, the frame material can contribute to ride quality. The cheaper fat bikes are made from high-tensile strength steel and are very bouncy because the frame is flexible. The better fat bikes are made from chrome-moly alloy steel and are less-bouncy because of a stiffer frame.
My fat bike's frame is made from hydro-formed 7051 heat-treated aluminum alloy. My fat bike's frame is stiff and light. The 9:Zero:7 is not bouncy and, as a bonus, the stiff frame makes the bike very responsive to steering input. As a matter of fact, the 9:Zero:7 is fairly touchy for a fat bike.