Google just released a pretty cool feature for their Customized Search Engine (CSE) creator. For those of you unfamiliar with the CSE it is just a way for users to create their own search engine that returns results only from the sites they specify. For example, you could make a technology search engine that only queries technology websites for results, and all you would have to do is provide the URL’s of those sites.
The new feature that was added for the Customized Search Engine lets users include the sites listed as well as the sites they link to. To demonstrate this I’ve created a search engine for our site that will also search all of the sites we link to. Then if you do a search, such as this one for "review," you’ll notice that the results included are not just for our site.
You can also go to the "On the Fly" site and type in the URL of the site you want to test out. This is an easy way to see what this feature might be like on your site because it doesn’t require that you fill out information prior to doing a search. If you like how it turns out just grab the code they provide on that page and paste it into your site.
This feature adds a lot of possibilities to the existing Customized Search Engine, and this is something users will probably start to take advantage of. If you use this in conjunction with the Google Marker you could probably develop some pretty nifty search engines.
Source: Google Custom Search Blog