I have had mine for about 15 years. I have hundreds and hundreds (and hundreds) of dies. My husband and I built a counter height 4 X 14' table with storage beneath. 36" high seems to work best for me. I used to make cards, invitations, party favors etc. (hence my name PAPERPrincess), before I got into quilting. The dies are best stored on edge to minimize any damage to the blades, which actually is pretty hard to do. I've purchased boxes of dies where they were just thrown in there and there were no problems. The one thing that CAN damage your dies is not keeping the joins clean. There are tiny areas where the blades meet. threads or bits of paper can get wedged in there and if you don't clean them out they eventually will force the blades apart, distorting the shape. It's a good idea to inspect your die every time you put it away to make sure that it's clean.
Before building the table, I used milk crates to hold the dies. stored them upright.