Histograms have become an invaluable tool when assessing exposure. Combined with the ability to pick at a photo you just took, they have replaced the use of a light meter for many photographers. This is true for video as well as stills.
Photographer and videographer Cédric Hauteville started a new web series and his first episode deals with Histograms For Video. He covers the obvious like what a histogram is and how to use it, but also some more advanced topics like the importance of looking at a histogram along with the photo, and how to use histograms to judge the white balance settings.