I run front chains only as well. They help tremendously for steering when there is snow on the ground, and the extra traction they provide is amazing. I've heard stories about how much potential damage running just chains in the front can do, but I do not understand them. I often times disengage 4WD (in the winter while running my front chains) just to see if there is a lot of stress on the drive train, and it always slips out of 4wd with no problem. If I was having a problem of different wheel diameters (hence, different ratios) due to the chains, I would feel a lot of resistance while disengaging 4WD... but I never do. Of course, your experiences may differ, but based on my experience, running chains on the front only is not a problem.
Corm