For me, the fact that it's a conversation — rather than just a one-man talk — makes it more engaging. I tend to tune out a bit when it's just one person talking

For me, the fact that it's a conversation — rather than just a one-man talk — makes it more engaging. I tend to tune out a bit when it's just one person talking (remnants of my University years?), but always snap back into focus when the second person joins in. Also, in the case of the MapReduce video, it feels helpful to have the concepts repeated in slightly different words. If you understood the idea the first time, it reinforces it. In case you didn't quite get it the first time, it gives you a second chance.