This Compete blog post argues that most of the search query volume at the major search engines is driven by a relatively small number of search engine users: power searchers. According to Compete, “[T]he top 1% of searchers performs a full 13% of all searches in a given month.” Breaking this out by engine, Compete says, “70% of search queries in September were performed by 20% of Google searchers. For Yahoo! the concentration increased to 73% and for MSN/Live searchers 75% of the queries were performed by the top 20%.”
There’s more analysis that needs to be done, especially regarding the SEM implications of all this (assuming the Compete data and analysis are correct). For example, if most of the search queries are being performed by a comparatively small and sophisticated segment of the audience, then some of the search spend could well be wasted.