Carving up the world of search... 
Google says..."Create a highly specialized Custom Search Engine that reflects your knowledge and interests. Place it on
your website and, using our AdSense for Search program, make money from the resulting traffic".
- Place a search box and search results on your website.
- Specify or prioritize the sites you want to include in searches.
- Customize the look and feel to match your website.
- Invite your community to contribute to the search engine.
(from Google Custom Search Overview).
Create Your Own Custom Search Engine
It's as easy as 1, 2, 3...4, 5.
1. Get a Google Account
2. Name and describe your search engine
3. Add keywords
4.Provide a list of sites
5. Customize
Strengths and Weaknesses of Google's Custom Search Engines