By Jon Mitchell at the inimitable readwrite (ReadWriteWeb), a good, basic description of "How Google Search Really Works."
Among the things that caught my eye were the following: 
- "Today, with real-time search, that can happen in some cases in less than a minute." Back in the day, it might take search engines weeks to find and index your pages/site; there were actually facilities to submit your pages/site to an engine for higher priority indexing.
- "16% to 20% of queries that get asked every day have never been asked before." I would never have supposed it was that high -- I would have guessed 5% or so.
As I come across additional pieces concerning how search works, I'll post them at follow-ups.