Mike Gerra authored a detailed analysis of social search technologies and their impact on the travel vertical. It can be purchased via Phocuswright.
The synopsis from Phocuswright:
Social search holds big promise for the travel sector, offering more relevant results for consumers and better targeting prospects for travel marketers. This article examines the various flavors of social search and recommends steps marketers can take to refine their search strategy and prepare for the next generation of social search engines.