Always on has a great post on this debate. Here is what he has to say:
One thing that I wonder about is how will viewers click to find the site of the advertiser? Is this important? Isn't this a key way that advertisers determine the success of a campaign? Will click-throughs be some sort of metric to successfully measuring the effectiveness of video advertising?
To sort this out, we invited Greg Stuart, president of the Interactive Advertising Bureau, the trade association for all the major online publishers, to our Manhattan studios to ask him a thing or two about click-throughs and online video.
http://video.google.com/googleplayer.swf?docId=3105273564746470335&hl=en