So I just need to go 'on record' on something that I see every day that bugs me regarding the term 'search engine'. Back in the day, a search engine was the core piece software that let you perform search on one or more sites - software like Verity, Fulcrum, Convera, Excalibre, and the granddaddy of all web search technologies, WAIS.
Sites like Altavista, Yahoo, and Google were search sites, not search engines. In fact, for a while there the search engine that powered Yahoo was Google.
The good news is that search engine companies like FAST Search, Autonomy, IBM Omnifind, Lucene, and even the Google Search Appliance (and others) have evolved and adopted a new name for what they offer - 'enterprise search', or even 'search platforms'. It is these products - what I'd call search engines if I were as old fashioned as my age might suggest - that are the site search engines of today.
There, I've said it.