This article talks about ad spending and economic growth. As a point of note, it points out that marketing organizations spend about 7.5% of their marketing budgets (I presume they mean "advertising" budgets) on the internet even though people devote about 20% of their media consumption to internet-based media.

http://www.economist.com/research/articlesBySubject/displaystory.cfm?subjectid=348963&story_id=10567459#top