For the last several years, search engine marketing has been on a tear. While the big advertisers sat on the sidelines in the beginning, they have lately been ramping up their spend on pay-per-click advertising, primarily on search engines but also affiliate sites like those that run Google Adsense.

Still, Steve Rubel believes the PPC market is nearing its all time high, and lists the following five reasons for a possible cool down of the market:

- Ad Clutter
- Declining Relevance of Traffic/Transition to Cost Per Action
- Rising Costs
- Marketers venturing for other forms of advertising, namely social media marketing
- Search Ads Are Viewed as Untrustworthy

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