Search algorithms & popularity factors: link, social, click, blog, industry. Since modern search engines are concerned with popularity and not direct relevancy, & big firms up the price of text link buying beyond affordability...
There's clear demand from searchers who increasingly expect user reviews as part of their local search experience. Social and local search are on a clear path towards merging.
This plugin is streamlined for some best practices for Wordpress SEO. While it gives you many options the defaults reflect the settings I recommend using.
J. Griesbaum. Generation International - die Zukunft von information, Wissenschaft und Profession. Proceedings der 31. Online Tagung der DGI, page 157-170. Frankfurt a.M., DGI, (2009)