I bought a bunch of quarter-sawn Sycamore really cheap (about $1.00/bf) a while back. It was frequently used as a secondary wood, and I figure I now have a lifetime supply of it.
IMO secondary wood should be QS so you can build your drawers with close tolerances and there's less worry about cupping/warping etc... Stability should be the primary concern. I think I read somewhere that Pine was a popular choice because it is more stable than most hardwoods, particularly if they aren't QS.
"History is strewn with the wrecks of nations which have gained a little progressiveness at the cost of a great deal of hard manliness, and have thus prepared themselves for destruction as soon as the movements of the world gave a chance for it." -Walter Bagehot