Finding a monetization model for YouTube is a top priority for executives at Google. But the man charged with leading that effort, Shashi Seth, won't be around to offer his insights.

On Tuesday, blogger Om Malik reported that Seth had quit YouTube to become the CRO at Cooliris, a startup that's working on a new photo browser. CNET confirmed that report today.

While Google has more than 20,000 employees, it has seen an exodus of key executives in recent months. That trend has raised questions about whether the search giant will be able to extend its lead to other segments of the online advertising business. More troubling for Google, while some of those executives are leaving for startups, others are finding new homes at places like Facebook.

As for YouTube, the video destination is not without assets. Despite an onslaught of challengers, YouTube has managed to hold its No. 1 spot atop the heap. Perhaps more encouraging, YouTube has managed to become a serious contender for the web's advertising dollars. That trend, which has been partly the result of experiments from major brands like Toyota, could also be attributed to an increased push from YouTube to rollout tools for advertisers, including a new demographic component to its analytics reporting.

While YouTube will remain committed to rolling out new products to help advertisers, Seth's departure will certainly make that process more difficult.