FreshDV has made available a streaming/download video tutorial Understanding Depth of Field by Justin Snodgrass. It's a "20 minute video provides a detailed explanation of depth-of-field and the factors that affect it. This tutorial was designed specifically for filmmakers who use or are planning to use 35mm depth-of-field adapters."
FreshDV also has an in-depth video series on The Art of Pulling Focus, taught by a seasoned First AC with 30 years of filmmaking experience.
Update: There more info at The Ultimate Depth-of-Field Skinny, an article by Jeff Donald at DVinfo.net.