Specs for search engines?

[KAREN SCHNEIDER]

If you were going to purchase a search engine for your
rapidly-growing library website, with an eye to delivering a large
number of electronic documents and other resources to a
heterogenous community, what would you look for?  

Or, put another way--am I on the right track here?  

*  It should support structured and unstructured searches
*  It should have highly configurable output
*  It should kick butt.  ;-)

Karen G. Schneider/US EPA Region 2 Library
schneider.karen at epamail.epa.gov
opinions mine alone