Linus Gregoriadis of E-consultancy recently published a shopping comparison engine buyer's guide focusing for the UK market. E-consultancy estimates that shopping comparison engines made between £120m and £140m in UK revenue during 2005.
One of the most telling facts testifying to the popularity of shopping comparison engines is comScore UK's data which reveals that "shopping comparison engine sites now have 49% reach within the UK online population."
Linus dedicates an entire section to using the comparison engines effectively, and I was particularly interested in the optimization techniques for merchants advertising on the shopping comparison engines. He covers the importance of tracking, deep linking, and the tendency of marketers to abandon the marketing channel prematurely. See my comments at ComparisonEngines.com.
Linus also does a SWOT (Strengths Weaknesses Opportunities Threats) Analysis and covers the following topics: Market Consolidation, Reliance on Google, and Increased Merchant Understanding of Comparison Engine ROI.