I had them on my last RAM and they were one of the main reasons I wanted another RAM. I don't know if they are going to warp or not but even the warping issues I have seen haven't looked like a big deal. Yes, if you are getting your truck as a show truck and never actually intend to do truck things with it then I can see you being upset if your Ramboxes are off by 1/8th of an inch but that isn't why I have a truck. As to them taking up bed space, the bed is no more narrow than the space between the wheel wells in a none Rambox truck and you definatley don't give up bed length or height like you do with a toolbox and you don't have to worry about digging things out from under them like you do with a toolbox or with Diamondbacks bin.
As for me, I keep one side pretty empty except for an umbrella that I can grab quickly if needed, and then put my long guns in there when I go hunting or shooting. The other side has tools, tire repair kit, ratchet straps, trailer hitch, paper towels, Styrofoam cups, etc. in there. I haven't seen anything on any other truck to rival them.
Probably one of the biggest reasons you don't see them more is the expense, if you haven't had them or don't see the real usefulness then you aren't going to shell out what they cost, Especially now that the divider is not included in the price.