The problem with the lead-in video is worse than a TV commercial, IMHO. On TV you go to watch a program, and the ads are an annoyance but you wait for them to be over and then the program starts at a fixed time, if you're not watching DVR, eg I usually watch a news program in the evening. But on YouTube, you make a selection of the video you want to watch next, and then instead some craptastic advert appears first. I don't understand why advertisers think this is a good way to reach people; yes, you get their attention by appearing as a surprise, but now consumers associate the brand with concepts like interruption and unmet expectations, before they begin processing any of teh semantic content of the ad. I frequently don't even notice what the ad is for because after the initial annoyance, my attention is fixated on finding the Skip button and counting down the few seconds before I can click on it. Many ads haven't introduced any product or branding by the time I skip away, and those which did so have already generated a reflexive mutter of 'Fuck off, Brand_owner!'
Now that I mention this, just thinking about previous Youtube ad annoyances brings several specific brands to mind, brands which I would otherwise feel neutral about because I've never purchased any products from them. Instead they're now firmly coupled with swear words. Think about that if you're ever considering a video ad campaign; the people who click out early are probably not just disinterested, but may actively resent your brand and your campaign might result in a net loss of business.