Stumbled across a great feature for ecommerce/portal/information websites recently.

In a nutshell, if you are using Firefox or Internet Explorer, you probably have a search box in the top right-hand side of your browser. In which case you can add your site to the list of sites that this search box will search... So instead of defaulting to live.co.uk or google.co.uk your search could also encompass a variety of websites.

A simple explanation can be found here: http://remark.wordpress.com/articles/quick-architecture-extending-reach-with-a-search-provider/ 

This functionality uses OpenSearch technology which has been pushed by Amazon/A9/Alexa for a few years - www.a9.com

[EDIT]

Combine this with the new features of the next generation of browsers, and you've got some pretty useful tools http://blogs.msdn.com/ie/archive/2008/09/15/what-s-new-for-ie8-search.aspx