Very cool idea and thank goodness somebody realized that there needs to be an insert row/column for grids (when is this going into Blend?). Looks like it was really well executed, too, so thanks for all of that.
On the other hand, I think that whoever edited the video needs to understand that there is zero interest in watching two guys staring at a laptop, and FAR more interest in what is actually going on in the screen of that laptop. After the typing began and before the final "goodbyes", I was extremely frustrated as he did who knows what to actually create the XAML because I was looking at him talking about it rather than the screen when that occurred. Ditto for lots of other key points in the demo. There was never a point where I was really curious about what it looked like to see them talking, so keep the camera on the screen please.