A misguided thought people often have is that it's okay to pour grease down a garbage disposal. The disposal does not have a special mechanism inside of it that destroys the grease, and the blades won't have much effect either. Instead, the blades will become less effective after repeated coatings of grease.
A few warning signs that will alert you of an impending blocked drain include slow drainage, gurgling noises coming from the drain, and a bad smell. If you can't seem to get rid of the clog yourself, call in a plumberto take care of the problem.