LOL....cinder blocks have been a mainstay for most of my tank stands for decades! With 4x4 runners underneath the tanks, I've never had to worry about instablity or warping...and this includes living through the Loma Prieta earthquake......if I need to make up for any minor irregularities, I use styrofoam or indoor/outdoor carpet remnants under the tanks to even things out....cinderblocks, duct tape and bungee cords....the big three......without them, there is no civilization....
Yea, but the thing is that the wood does not support all the seams underneath the tank and there are open spots..Like here is an example of a DIY cinder block stand:
http://saltaquarium.about.com/od/algaemarineplantcare/l/bldiyaqstand.htm