I just got some new racks with back heat from reptile basics. It's my first back heat setup, and i'm pretty sure i will stick with it from now on. Here's what Rich from reptile basics had to say about back heat:

" Which is better? We have found back heat to be every bit as effective, if not more so, than belly heat. The back heat in these racks will easily warm the back 1/3 to 1/2 of the boxes to a cozy 88-90 degrees. Actually it will get hotter than that if you don't use a thermostat or rheostat which is why one is required. The heat tends to be more even than belly heat which is usually in a more concentrated 3"-4" wide strip across the bottom. The heat gradually tapers off to about 80-82 in the front of the box. Our animals very easily thermoregulate with this setup and we have switched over to entirely back heated rack systems here.
Is belly heat bad? We dont think so, we just like this better. If you will be setting up a 32 Qt. Sweater Box Rack in a room that is regularly below 74 degrees you may want to consider the belly heat option. On a Shoe box or MCB-S tubs the back heat will provide great performance in all but the coolest of rooms (below 65 degrees). One note, with belly heat racks you MUST place your thermostat probe on the heat tape itself. NOT inside one of the tubs. On the CB-70 rack we install belly heat standard. The extra long CB-70 makes back heat ineffective."

All in all i think it's different strokes for different folks, and after using both i'm in the back heat club!