In order to help better understand the visitors to your web site and what information they need from you, many people suggest adding a search facility.  When people arrive at your site and don't find what they need right away, they can search for the information they want rather than trawl through the whole site. 

Having a search engine also means that you can track the keywords that people are using.  This can be useful to ensure that popular topics are more prominently displayed on your site and to highlight voids in content for the questions/keywords that do not yield any results.

Up until recently, adding a search capability to your site meant that you needed to use a CMS or develop a search engine script yourself to index and search your entire site.  These approaches seemed to always fall short of the power of everyone's favourite search engine - Google.  Not any more.

Google is now offering a version of its Custom Search capability called "Custom Search Business Edition" and for $100 per year they will allow you to index up to 5,000 pages on your site - all without the previous requirement of displaying their ads in the results.

There are lots of other nifty features too:

1. No Ads!  Previously, you could add Google search to your site using their Google Co-op facility.  It was nice and easy, but many people refused to implement it on their web site as you were required to display adwords ads in the search results (without compensation).

2. Easy Customisation.  For novice users, you can customise the search interface by changing fonts and uploading logos - all within their set up screens.

3. XML Results.  For more advanced users, Google will return the search results in XML.  This means that these results can be manipulated easily with technologies such as XSL to render a more seamless integration into your web site.

4. Reports.  As mentioned above, this is where you can get some priceless information about how people use your web site.  Which keywords are being used, etc.  Once you have this information, you really need to use it as a feedback mechanism to improve the usability of your web site.

There are a few other features not mentioned above such as support for multiple languages, etc.

We're currently re-developing our own web site and will certainly be taking advantage of this technology from Google in the new site.  If you haven't already built search into your site, then I would recommend you consider doing so - it will help make your site more usable and provide you with a great way to help meet the needs of your visitors.