Here's a pretty good talk about restricted Boltzmann machines by Geoffrey Hinton. He explains the concepts and problems very well and basically without maths:
His Neural Networks for Machine Learning course¹ is quite a pleasant journey going into everything from simple perceptrons to RBMs, and DBNs² and their uses. As a bonus he's got a quirky sort of dry humour that kept things interesting.
1: https://www.coursera.org/course/neuralnets
2: http://en.wikipedia.org/wiki/Deep_belief_network