Informality can waste time
One of the down sides to informal videos, and a pet peeve of mine, is the tendency of presenters to waste the viewer's time. Video bloggers, I do not need or want to see you set up the camera. I don't care about your technical difficulties. If you shoot some material that isn't relevant, do a favor to every single person who will watch your video, and edit it out! The same goes for poorly organized and presented material. If you can't say it clearly and concisely, do a retake!

Duff's informal video does a nice job of presenting the context (Duff making breakfast, and the reason he shot the video during that time) without burdening the viewer with unnecessary fluff.

Results of some relevant experiments I did
Throughout 2009 I experimented with presenting myself in various ways at parties, social events, workshops, and on dates. I dressed more or less formally, sexily, sensually; I did or didn't wear/carry clothes and props that nonverbally signaled my interests; I interacted with people in various ways.

Rather than testing formal vs. informal behavior, I played with how and when I approached people. For instance, introducing myself to other students before a workshop began vs. approaching people during and afterward. Introducing myself to everyone, systematically, vs. approaching people individually when they said or did something interesting. Saying hi to everyone I knew, vs. saying hi only if we crossed paths during the event. Introducing myself only, vs. also introducing the person I had just spoken to.

Unsurprisingly, I discovered that I get more of the responses I want when I dress and act in ways that are congruent with the outcomes I want. For instance, if I want to meet potential dates at a party or workshop:

1. I wear something socially appropriate, so I fit in the context and people feel comfortable with me.
2. I wear something that looks both pretty/sexy and touchable, so people will find me visually attractive and also want to touch me.
3. I am friendly and smile a lot, which makes me more approachable.
4. I introduce myself to everyone I can, as early as I can. Once people talk with me, even briefly, they are much likelier to approach me later, and to introduce me to others.
5. I do fun things with people that make them and me smile. I have fun, they have fun, they enjoy being around me and tend to come back. And as a side benefit, other people see me surrounded by smiling people and figure I might be worth approaching.

By behaving this way, I meet and gain rapport with many more people, make far more friends, and find probably 20 times more potential dates. Or they find me, LOL!

I don't regard any course of behavior as more or less "authentic." Virtually all human behaviors are arbitrary and constructed! However, some behaviors work better to get the outcomes I want, which aligns better with my values and goals. When I behave in ways that generate the results I want, I feel grounded, congruent, and alive. I have fun. And people respond well to me, as if I've got some kind of social magic. As if I'm, well… authentic.

Duff also provides fewer social rapport cues. The viewer can't really see whether he makes eye contact, but he rarely smiles, he doesn't move his body around in relation to the viewer's viewpoint, and he makes few social gestures toward the viewer. Verbally, he provides much less context for his presentation.

For most of us, formality is a signal to not engage passionately and connect with deep rapport. We've all had lots of exposure to "talking heads" on video, and Duff presents himself as one.

These factors all work against establishing emotional rapport with the viewer, or creating a strong emotional response in them that will make the video's informational content seem interesting, important, or worth remembering.

Framing and context
In Duff's informal video, rapport and social cues create a frame for the content that makes it seem relevant and interesting. Duff's formal video lacks these rapport and social cues. It is pretty much "about" its informational content. A viewer who has a burning interest in the information might find Duff's formal video riveting. For most people, the content alone won't be enough to create the same level of interest.

On the other hand, some people will interpret the lack of social cues in the formal video as meaning that Duff has high authority. Some of those folks might pay more attention to the content because of that.

It would be interesting to do another A/B test. In the informal video, Duff could dress and act casually, but speak in a monotone, mostly avoid eye contact, and not move much. (I have seen numerous bad YouTube videos like that.) In the formal video he could dress and act more formally, but speak and gesture animatedly, smile, and made lots of eye contact. I suspect people would find the latter more "authentic."

There's also the matter of context. Duff's making-breakfast video would probably go over poorly at a stuffy professional conference, because it mismatches people's expectations for that context. But for someone surfing the Web in their spare time (informal context), his breakfast video matches their expectations.

Bottom line: If you want to get your point across, engage your audience!