For most people, watching Web video is predominantly a streamed experience on your computer. But an important and substantial portion of Web video is still downloaded to be watched later, or transferred to a different screen (usually an iPod, but sometimes a flat-screen TV). The problem with downloads is that they don't fit neatly into the advertising model that rules most other Web video. Earlier today at the Beet.TV Online Video Summit (which I co-moderated with Cnet's Dan Farber and Beet.TV's Andy Plesser), blip.tv CEO Mike Hudack revealed that his company has found a way to dynamically insert ads from DoubleClick into video downloads on iTunes and elsewhere.