I was able to get some relatively straight slabs from some sweet gum logs, but it took a bit of effort when drying. I cut the slabs 1 1/2"+ thick, and then stacked and stickered them. I put the stickers 12" -15" apart, and then put 3,000lb cargo straps on every other sticker. I went out weekly for the first three months and tightened the straps as tight as I could get them by hand. They ended up drying for over a year before I used any of them. As a result, almost every slab was useable. When milling them down to thickness, I took about equal thickness material off of both sides until I was within about 1/8" of the final thickness, and then let sit for a few days before going to final. I had very little warping using this method. In non-climate controlled storage, the boards that I stopped about 1/8" shy had almost negligible warping.
Jim Creasman's description is spot on with my experiences working with it. I think because the wood is relatively soft, and the cells are cross-linked, it didn't seem to harbor internal stress after drying. Also, because the growth rings are not distinct like oak or ash, it doesn't dish out between growth rings when sanding. Be careful working around knots (i.e use sharp tools and work towards the knot center), because it can tear out a chunk otherwise. (When this happened to me, I just glued it back in and then finished the process after it had dried.)
Sweet gum was used as a secondary wood (i.e. drawer supports, corner blocking, etc) in much of the NC furniture back in the "Furniture Capitol" days.