Campaign Insights is a powerful tool that can give advertisers reliable data about how a campaign has raised brand awareness, or active user interest, in a particular product or service. Campaign Insights compares the impact of a campaign on a large groups of users who were exposed to a display ad campaign with impact on a similar group who weren't exposed to campaign. Specifically, it then calculates the incremental lift in both online search activity and website visits -- a good indicator of advertising effectiveness.
"Google now provide Campaign Insights results for some YouTube advertising campaigns that're reserved in advance (not bought in AdWords auction). We can currently only measure effects of relatively large campaigns, but we're working hard to expand this opportunity to smaller campaigns as well. Please contact your Google sales representative if you are interested in measuring the effectiveness of your YouTube campaign using Campaign Insights," explains Google.