Do Travel Search Engines Deliver?
http://www.consumerwebwatch.org/dynamic/travel-reports-aggregators.cfm

This article investigates 11 leading travel search sites for breadth, depth, usability and customer service. Expedia and it's main competitors are not included in the definition of a Travel Search Engine but this article does include some very interesting analysis of these smaller competitors.

Jeffrey Kelly
http://sailwhatcom.com