Usually recession takes out the trust of life blood of of economy out to a drive and after that it is a chain reaction, everything but essentials will fail. But in order to climb out of such a hole should it ever happen, will be harder. Even though Advertising and marketing may get cut first, you will have to advertise in order to promote your products in a awakening economy. Some will have to continue advertising in the best possible method to sustain continuity. So some advertising and marketing may get cut but search advertising (give them what they look for), CPC will live through as Don says, Advertising in general will fall, but CPC Internet advertising will increase.
"The trend towards Internet advertising has been growing for years. Still, less than 10% of all advertising dollars are spent on the Internet, up from about 6% a few years ago. The trend will continue and probably accelerate with a recession. This is great news for search engines like Google, Microsoft Live Search, and Yahoo Search."
In fact the recession might be a shot in the arm for internet advertising!