Web searching: back to basics
1) no search engine covers everything;
2) different search engines miss different things;
3) retrieving large numbers of results is not necessarily bad;
4) all search engines offer advanced search techniques to improve results;
5) meta-search engines are not the same as search engines;
6) Google is great but not the only search engine; and
7) be prepared for changes in all search engines.
This comes from Middle-Age (2002!) but seems still relevant.
Tenopir, Carol. Online Databases-The Web: Searchable, Hidden, and Deceitful. Library Journal, 2002