There have been a number of tweets going round Twitter over the last hour or so relating to combining a PPC and SEO strategy and figures for employing such a tactic. Google and Yahoo for obvious reasons will highlight the benefits of such a tactic, however there are a number of such studies in existance, and the evidence is quite compelling.
99% of C-level executives use the web at work.
52% of executives consider the Internet the most important source of information on business.
C-level execs are online somewhere between 115 minutes and 137 minutes per day.
Source: Harris Interactive & GartnerG2 Study, March 2005
Yahoo have one such example where the following evidence regarding holistic search marketing was producted
Google have a similar bit of research published however whilst the original Yahoo research targeted impact on clickthrough, the Google study was more involved in terms of brand perception and brand association.
Further research by Enquiro and Google continues to reinforce the benefits of a combined PPC/SEO strategy and the effect it has in terms of consumers willingness to purchase following engagement.
The full Enquiro/Google research whitepaper can be found via the Enquiro website (Highly recommended reading).
There are obvious niches where such tactics may not work, and it is often a case of testing (refining and testing again) however I would always advise caution when deciding to blanket turn off PPC once organic traction has been obtained. As the research above suggests, it may not always result in the best ROI.