I've been focused on and tinkering with video for the past week and a half so the discussion over ideal length for vlog video grabbed my interest. I  think vlog videos will, in the end, be both long and short, meaning short ones will be strung together into one or more series and long ones will be broken down into small ones, affecting organization and presentation of clips as well as planning, production, and post-production.
Scoble's interviews, for example, should be broken down into shorter clips, each focusing on a subject so that watchers can experience either the whole interview or just the parts that interest them. Turning long interviews into bite-sized segments allows easier navigation and reference as well as offering drive-by advertising opportunities between segments. Seen abstractly, segments adds fine-grained connection points and increases the surface area at the same time, making it easier to link to other contents and resources, both internal and external, and allowing social interaction at attention-grabbing level. For example, each segment could be given a discussion area (comments) so watchers can discuss at a subject level instead of having at the interview level. From traffic analysis perspective, segments give producers better feedback data for improving content and service with.
Unfortunately, today's vlogging tools has not evolved enough to support segmentation. But I expect that to change quickly.