According to a recent Study from Google, based on companies running adwords on both search and content networks, the cost-per-acquisition (CPA) is about 2% lower on the Content Network than on search pages, with the Content Network driving close to 20% of their total conversions.

Conversion Rate is generally much smaller than on the Search Network but with the CPC lower as well it does explain those figures.

I always advise my customers to run both Search and Content campaigns but separately for tracking purposes mainly. Once you can track the content network you can also run campaigns using the Placement network which is even more targeted.

Find more about this study Here.