Ditto what bakechef said. Better to only have a small piece of a well done cake than to have all of a substituted cake that tastes like...pumpkin or something. Blech.
Having said that, is the sugar your major concern or is it the fat? If you want to lower the fat, you can do that by subbing some applesauce for some of the fat. Not all, SOME. You lose taste and texture if you sub all of it out. If your concern is the sugar, well that's another story altogether. Sugar is sugar is sugar. Whether its in honey or brown or white, it has the same calories. You need to use Splenda if that is your concern.
You're only given a little spark of madness. You mustn't lose it. Robin Williams