As Doc Searls has noted, bloggers searching for old blog entries on their own blogs are failing to find them via Google search.
Here's how it works. I'm writing a blog post, and want to incorporate a link to something I previously wrote on my blog on the same topic, but can't remember where or precisely when I wrote it. I used to be able to find it via a Google search, but not for the past few months. Doc got around the problem by using Yahoo search.
As Doc says:
The fact that Google fails to find pages that have been sitting in plain sight of its crawlers for long periods of time, while Yahoo finds those same pages, is rather interesting data.