The resident PhD, Orion, over at the Search Engine Watch Forums, provides an insight into search engine optimization that many SEOs do not think about. In his latest thread named What is Keyword Competitiveness?, Orion says that two popular keyword analysis techniques used by SEOs are "based on speculations" and is an "exercise in futility."
The two methods he dislikes include: (1) Combining Google and Overture keyword volumes and (2) Building a composite metric from keyword tools that have data from "dissimilar meta engines". Well most of the tools we have use "dissimilar meta engines".
I'll quote his explanation and then you can battle it out at the thread.
Combining two different or more metrics, some representing document counts and others representing query volume from dissimilar databases (Google with Overture or several meta engines), seem to be an exercise in futility: e.g., two dissimilar analytics from two different stores are combined and taken for a fair metric. Surprisingly, many SEOs/SEMs use and defend this approach, even when the arguments are based on formulas made out of thin air. Purely and simply: based on speculations.