I thought about it. The reason I didn't do it is because you can only stain darker, not lighter. it would make for a dark floor, and it would make the the whole room look dark. It's hard enough to get enough light in a garage as it is, without making the floor darker. Go into two equally-lit garages, one with a dark floor and one with a light floor, and you'll be amazed how dark and dingy the dark-floored garage feels.
MHO, YMMV, flame suit on.