How much of the CPC and CPM ad market depends on interest rates? More than you may think since mortgage re-financing ads comprise at least 20% of ad volume in total dollars. The high prices of mortgage related ads mean they contribute a lot to the bottom line of Yahoo and Google.
This graph from searchnewz puts the Fathom Online keyword pricing survey into perspective. The red line represents the cost of mortgage related keywords, and they are at least twice as expensive as any other category. I wonder how much of Google's and Yahoo's recent quarterly profits were directly from mortgage ads. I'd guess at least 35%.
The funny thing is that the internet itself can take some credit for low interest rates (remember "The New Economy"?). The internet is largely responsible for a higher productivity increase over the last 10 years which has helped the economy, kept inflation at bay, and helped convince Alan Greenspan to not raise rates as fast as he otherwise might have.
However, the mortgage refinancing process is fairly cyclical. As it begins to wane, it's unlikely that any other category will replace it's total contribution to profits. Isn't it?