A fresh approach at some analysis of which search engine has a more comprehensize index: A Comparison of the Size of the Yahoo and Google Indices. It would be interesting to see this study at another order of magnitude, perhaps with MSN included. What I like best is that the study authors released the code for the tests. I seem to be finding that more academics are providing code to let others attempt to verify their study firsthand, build on the study to make relatable comparisons, and most importantly to prodive the opportunity for peer review of the code logic of what the study claims.