Phil Bradley points to this research paper, The Freshness Of Web Search Engines' Databases (PDF), out of Heinrich-Heine-University in Dusseldorf that analyzed the freshness of Google, Yahoo and MSN over six weeks in February and March 2005. Google came out best with the most pages updated almost daily, but MSN had the best "worst case" scenario with no page more than 20 days old. Yahoo was said to be "chaotic." There's much much more in the paper which, sadly and ironically, is already out of date in terms of knowing what's happening right now. But having benchmark for various points in time is great.
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