I've changed the lucene-based search to require all given terms to match by default. This gives more focused results and is more consistent with typical search engine practice, and our behavior under the old MySQL search.
You can still make terms optional by explicitly using the 'OR' operator such as: "civil OR war", "blueberry OR pie". (Note that 'OR' must be capitalized.)
-- brion vibber (brion @ pobox.com)