Deep belief networks are extremely powerful, we are finally getting to the point where we don't need to do tons of feature engineering to make useful complex classifiers. Used to be you would have to spend a ton of time doing data analysis and feature extraction to get useful and robust classifiers. Of course the usefulness of those sorts of networks were limited by how well you did the feature extraction. Now you train networks with much more minimally processed data, and get great results out of them.